Unit 4 Biology

Front 1

Habitat:

Back 1

1) The place where an organism lives, e.g. a rocky shore or a field.

Front 2

Population:

Back 2

1) All the organisms of one species in a habitat.

Front 3

Community:

Back 3

1) Populations of different species in a habitat make up a community.

Front 4

Ecosystem:

Back 4

1) All the organisms living in a particular area and all the abiotic conditions, e.g. a freshwater ecosystem such as a lake.

Front 5

Abiotic Conditions:

Back 5

1) The non-living features of the ecosystem, e.g. temperature and availability of water.

Front 6

Biotic Conditions:

Back 6

1) The living features of the ecosystem, e.g. the presence of predators or food.

Front 7

Niche:

Back 7

1) The role of a species within its habitat, e.g. what it eats, where and when it feeds.

Front 8

Adaptation:

Back 8

1) A feature that members of a species have that increases their chance of survival and reproduction, e.g. giraffes have long necks to help them reach vegetations that's high up. This increases their chances of survival when food is scarce.

Front 9

Species Occupy Different Niches:

Back 9

1) Every species has its own unique niche.
2) If two species try to occupy the same niche, they will compete with each other. One species will be more successful, until only one species is left.

Front 10

Natural Selection:

Back 10

1) Organisms with better adaptations are more likely to survive, reproduce and pass on the alleles for their adaptations, so the adaptations become more common in the population.
2) Organisms are adapted to both the abiotic conditions and the biotic conditions in their ecosystem.

Front 11

Adaptations to Abiotic Conditions:

Back 11

1) Otters have webbed paws - they can both walk on land and swim effectively, so they can live and hunt on both land and in water, increasing their chance of survival.
2) Whales have a thick layer of blubber - this helps them to keep warm in the coldest seas, so they can live in places where food is plentiful, increasing their chances of survival.

Front 12

Adaptations to Biotic Conditions:

Back 12

1) Sea otters use rocks to smash open shellfish and clams - this gives them access to another source of food, increasing their chances of survival.
2) Some bacteria produce antibiotics - these kill other species of bacteria in the same area, reducing competition for resources and increasing their chances of survival.

Front 13

Investigating Populations of Organisms:

Back 13

1) Investigating populations of organisms involves looking at the abundance and distribution of species in a particular area.

Front 14

Abundance:

Back 14

1) The number of individuals of one species in a particular area.
2) The abundance of mobile organisms and plants can be estimated by simply counting the number of individuals in samples taken. Other measures of abundance include:
3) Frequency - the number of samples a species is recorded in, e.g. 70% of samples.
4) Percentage cover (plants only) - how much of the area you're investigating is covered by a species.

Front 15

Distribution:

Back 15

1) This is where a particular species is within the area you're investigating.

Front 16

Random Sampling:

Back 16

1) Choose an area to sample.
2) Divide the total area into a grid and use a random number generator to select coordinates.
3) Use an appropriate technique to take a sample of the population.
4) Repeat the process to increase reliability.
5) The number of individuals for the whole area can then be estimated by taking an average of the data collected and multiplying it by the size of the whole area.

Front 17

Pitfall Traps:

Back 17

1) Pitfall traps are steep-sided containers that are sunk in a hole in the ground. The top is partially open.
2) Insects fall into the container and can't get out again - they're protected from rain and some predators by a raised lid.
3) The sample can be affected by predators small enough to fall into the pitfall trap though.

Front 18

Pooters:

Back 18

1) Pooters are jars that have rubber bungs sealing the top, and two tubes stuck through the bung.
2) The shorter tube has mesh over the end that's in the jar. The longer tube is open at both ends.
3) You inhale through the shorter tub with the long tube over an insect to suck it into the jar.
4) It can take a long time to get a large sample. Some species may be missed if the sample isn't large enough.

Front 19

Quadrats:

Back 19

1) A quadrat is a square frame divided into a grid of 100 smaller squares by strings across the frame.
2) Quadrats are placed on the ground at different points, and are used to measure species frequency or the number of individuals of each species. It can also measure percentage cover.
3) Quadrats are useful for quickly investigating areas with plant species that fit within a small quadrat - areas with larger plants and trees need very large quadrats.

Front 20

Transects:

Back 20

Transects are used to find out how plants are distributed across an area.
1) Line Transects - a tape measure is placed along the transect and the species that touch the tape measure are recorded.
2) Belt Transects - quadrats are placed next to each other along the transect to work out species frequency and percentage cover along the transect.
3) Interrupted Transects - instead of investigating the whole transect of either a line or a belt, you can take measurements at intervals.

Front 21

Beating Trays:

Back 21

1) A beating tray is a tray or sheet held under a plant or tree.
2) The plant or tree is shaken and a sample of insects fall onto the beating tray.
3) You can take large samples using beating trays, giving good estimates of the abundance of each species.
4) However, the sample may not be random because most of it will be made up of insects that fall easily.

Front 22

Mark-Release-Recapture:

Back 22

1) Capture a sample of a species using an appropriate technique, and then mark them in a harmless way.
2) Release them back into their habitat.
3) Wait a week, then take a second sample from the same population.
4) Count how many of the second sample are marked.
5) Then use this equation to estimate the total population size:
total population size = number caught in first sample x number caught in second sample / number marked in second sample.

Front 23

Factors Affecting Accuracy of Mark-Release-Recapture:

Back 23

1) The marked sample has had enough time and opportunity to mix back in with the population.
2) The marking hasn't affected the individuals' chances of survival, and is still visible.
3) Changes in population size due to births, deaths and migration are small during the period of the study.

Front 24

Risk Assessment:

Back 24

1) When carrying out fieldwork to investigate populations you expose yourself to risks.
2) You need to think about what risks you'll be exposed to during fieldwork, so you can plan ways to reduce the chance of them happening.
3) Examples include: falls and slips, bad weather, stings and bites, etc.

Front 25

Ethics of Fieldwork:

Back 25

1) All fieldwork affects the environment where it's carried out, so investigations should be planned to have the smallest impact possible.
2) Some fieldwork affects the organisms being studied, so investigations should be planned so that organisms are treated with great care, and are kept and handled as little as possible. They should also be released as soon as possible after being captured.

Front 26

Abiotic Factors on Population Size:

Back 26

1) Population size is the total number of organisms of one species in a habitat, and it varies because of abiotic factors, e.g. amount of light, water, space, etc.
2) When abiotic conditions are ideal for a species, organisms can grow fast and reproduce successfully.
2) When abiotic conditions aren't ideal for a species, organisms can't grow as fast or reproduce as successfully.

Front 27

Interspecific Competition:

Back 27

1) Interspecific competition is competition between different species for the same resources.
2) It can mean that the resources available to both populations are reduced, limiting both populations by a lower amount of food, and so limiting the population sizes.
3) If one species is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.

Front 28

Intraspecific Competition:

Back 28

1) Intraspecific competitions is competition within a species for the same space and food.
2) Eventually, resources such as food and space become limiting - there isn't enough for all the organisms, causing the population to decline.
3) A smaller population then means that there's less competition for space and food, which is better for growth and reproduction - population starts to grow again.

Front 29

Predation:

Back 29

1) Predation is where an organism (the predator) kills and eats another organism (the prey).
2) The population sizes of predators and prey are interlinked - as the population of one changes, it causes the other population to change.

Front 30

Link Between Predators and Prey:

Back 30

1) As the prey population increases, there's more food for predators, so the predator population grows.
2) As the predator population increases, more prey is eaten so the prey population then begins to fall.
3) This means there's less food for the predators, so their population decreases, and so on.

Front 31

Birth Rate:

Back 31

1) The number of live births each year for every 1000 people in the population.
2) For example, a birth rate of 10/1000 would mean that in one year there were 10 live births for every 1000 people.

Front 32

Death Rate:

Back 32

1) The number of people that die each year for every 1000 people in the population.
2) For example, a death rate of 10/1000 would mean that in one year there were 10 deaths for every 1000 people.

Front 33

Population Growth Rate:

Back 33

1) Population growth rate is how much the population size increases or decreases in a year.
2) population growth rate = birth rate - death rate

Front 34

The Demographic Transition Model:

Back 34

1) The Demographic Transition Model (DTM) is a graph that shows changes in birth rate, death rate and total population size for a human population over a long period of time.
2) It is divided into 5 stages.

Front 35

Demographic Transition Model - Stage 1:

Back 35

1) Birth rate and death rate fluctuate at a high level. The population stays low.
2) Birth rate is high because there's no birth control or family planning and education is poor.
2) Death rate is high because there's poor health care, sanitation and diet, leading to starvation and disease.

Front 36

Demographic Transition Model - Stage 2:

Back 36

1) Death rate falls, birth rate remains high. The population increases rapidly.
2) Death rate falls because health care, sanitation and diet improve.
3) Birth rate remains high because there's still little birth control or family planning.

Front 37

Demographic Transition Model - Stage 3:

Back 37

1) Birth rate falls rapidly, death rate falls more slowly. The population increases at a slower rate.
2) Birth rate falls rapidly because of the increased use of birth control and family planning. Also, the economy becomes more heavily based on manufacturing rather than agriculture, so fewer children are needed to work on farms.

Front 38

Demographic Transition Model - Stage 4:

Back 38

1) Birth rate and death rate fluctuate at a low level. The population remains stable but high.
2) Birth rate stays low because there's an increased demand for luxuries and material possessions, so less money is available to raise children. They're not needed to work to provide income, so parents have fewer children.

Front 39

Demographic Transition Model - Stage 5:

Back 39

1) Birth rate begins to fall, death rate remains stable. The population begins to decrease.
2) Birth rate falls because children are expensive to raise and people often have dependant elderly relatives.
3) Death rate remains steady despite continued health care advances as larger generations of elderly.

Front 40

Population Growth Curves:

Back 40

1) Population change can be shown by a population growth curve. They're made by plotting data for population size against time.
2) Growth curves show whether the population was increasing or decreasing by the direction of the curve.
3) The steepness of the curve indicates the speed of change. You can also use the curve to calculate the rate of change.

Front 41

Survival Curves:

Back 41

1) Survival curves show the percentage of all the individuals that were born in a population that are still alive at any given age. This gives a survival rate for any given age.
2) Life expectancy is the age that a person born into a population is expected to live to - it's worked out by calculating the average age that people die.

Front 42

Age-Sex Pyramids:

Back 42

1) Population structure can be shown using age-sex pyramids. These show how many males and females there are in different age groups within a population.

Front 43

Biological Processes Need Energy:

Back 43

1) Plants need energy for things like photosynthesis, active transport, DNA replication, cell division and protein synthesis.
2) Animals need energy for things like muscle contraction, maintenance of body temperature, active transport, DNA replication, cell division and protein synthesis.

Front 44

Photosynthesis:

Back 44

1) Photosynthesis is the process where energy from light is used to make glucose from water and carbon dioxide (the light energy is converted to chemical energy in the form of glucose).
2) Energy is stored in the glucose until the plants release it by respiration.
3) Animals obtain glucose by eating plants (or other animals), then respire the glucose to release energy.

Front 45

Respiration:

Back 45

1) Plant and animal cells release energy from glucose - this process is called respiration.
2) This energy is used to power all the biological processes in a cell.
3) Aerobic respiration produces carbon dioxide and water, and releases energy.

Front 46

ATP:

Back 46

1) ATP is made from adenine, combined with a ribose sugar and three phosphate groups.
2) It carries energy round the cell to where it's needed
3) ATP is synthesised from ADP and Pi.
4) ATP diffuses to the part of the cell needing energy.
5) After being broken down, chemical energy is released from the phosphate bond and the ADP and Pi are recycled.

Front 47

Why ATP is a Good Energy Source:

Back 47

1) ATP stores or releases only a small, manageable amount of energy at a time (no energy is wasted).
2) It's a small, soluble molecule so it can be easily transported around the cell.
3) It's easily broken down - releases energy easily.
4) It can transfer energy to another molecule by transferring one of its phosphate groups.
5) ATP can't pass out of the cell, so the cell always has an immediate supply of energy.

Front 48

Metabolic Pathway:

Back 48

1) A series of small reactions controlled by enzymes, e.g. respiration and photosynthesis.

Front 49

Phosphorylation:

Back 49

1) Adding phosphate to a molecule, e.g. ADP is phosphorylated to ATP.

Front 50

Photophosphorylation:

Back 50

1) Adding phosphate to a molecule using light.

Front 51

Photolysis:

Back 51

1) The splitting (lysis) of a molecule using light energy.

Front 52

Hydrolysis:

Back 52

1) The splitting (lysis) of a molecule using water.

Front 53

Decarboxylation:

Back 53

1) The removal of carbon dioxide from a molecule.

Front 54

Dehydrogenation:

Back 54

1) The removal of hydrogen from a molecule.

Front 55

Redox Reactions:

Back 55

1) Reactions that involve oxidation and reduction.
2) If something is reduced it has gained electrons, and may have gained hydrogen or lost oxygen.
3) If something is oxidised it has lost electrons, and may have lose hydrogen or gained oxygen.
4) Oxidation of one molecule always involves reduction of another molecule.

Front 56

Coenzymes:

Back 56

1) A coenzyme is a molecule that aids the function of an enzyme by transferring a chemical group from one molecule to another.
2) A coenzyme used in photosynthesis is NADP, which transfers hydrogen from one molecule to another.

Front 57

Chloroplasts:

Back 57

1) Chloroplasts are small, flattened organelles found in plant cells.
2) They have a double membrane called the chloroplast envelope.

Front 58

Thylakoids, Grana, and Lamellae:

Back 58

1) Thylakoids (fluid-filled sacs) are stacked up in the chloroplast into structures called grana (singular granum).
2) The grana are linked together by bits of thylakoid membrane called lamellae (singular lamella).

Front 59

Photosynthetic Pigments:

Back 59

1) Chloroplasts contain photosynthetic pigments. These are coloured substances that absorb light energy needed for photosynthesis.
2) The pigments are found in the thylakoid membranes - they're attached to proteins. The protein and pigment is called a photosystem.

Front 60

Photosystems:

Back 60

1) There are two photosystems used by plants to capture light energy.
2) Photosystem 1 (or PS1) absorbs light best at a wavelength of 700nm and photosystem 2 (or PS2) absorbs light best at 680nm.

Front 61

Stroma:

Back 61

1) Contained within the inner membrane of the chloroplast and surrounding the thylakoids is a gel-like substance called the stroma. It contains enzymes, sugars and organic acids.
2) Carbohydrates produced by photosynthesis and not used straight away are stored as starch grains in the stroma.

Front 62

The Light-Dependent Reaction:

Back 62

1) This reaction needs light energy.
2) It takes place in the thylakoid membrane of the chloroplasts.
3) Light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy.
4) The light energy is used to add a phosphate group to ADP to form ATP, and to reduce NADP to form reduced NADP. ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction.
5) During the process, H20 is oxidised to 02.

Front 63

The Light-Independent Reaction:

Back 63

1) This is called the Calvin Cycle and it doesn't use light energy directly.
2) It takes place in the stroma of the chloroplast.
3) Here, the ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make glucose from C02.

Front 64

The Uses of Light Energy in the Light-Dependent Reaction:

Back 64

In the light-dependent reaction, the light energy absorbed by the photosystems is used for 3 things:
1) Making ATP from ADP and Pi. This reaction is called photophosphorylation.
2) Making reduced NADP from NADP.
3) Splitting water into protons, electrons and oxygen. This is called photolysis.

Front 65

Four Stages of Non-Cyclic Photophosphorylation:

Back 65

1) Light energy excites electrons in chlorophyll.
2) Photolysis of water produces protons, electrons and oxygen.
3) Energy from the excited electrons makes ATP.
4) Reduced NADP is then generated.

Front 66

Non-Cyclic Photophosphorylation - Stage 1:

Back 66

1) Light energy is absorbed by PS2.
2) The light energy excites electrons in chlorophyll.
3) The electrons move to a higher energy level.
4) These high-energy electrons move along the electron transport chain to PS1.

Front 67

Non-Cyclic Photophosphorylation - Stage 2:

Back 67

1) As the excited electrons from chlorophyll leave PS2 to move along the electron transport chain, they must be replaced.
2) Light energy splits water into protons, electrons and oxygen. (So the oxygen from photosynthesis comes from water.)

Front 68

Non-Cyclic Photophosphorylation - Stage 3:

Back 68

1) The excited electrons lose energy as they move along the electron transport chain.
2) This energy is used to transport protons into the thylakoid so that the thylakoid has a higher concentration of protons than the stroma, forming a proton gradient across the membrane.
3) Protons move down their concentration gradient into the stroma, via an enzyme called ATP synthase. The energy from this movement forms ATP from ADP and Pi.

Front 69

Non-Cyclic Photophosphorylation - Stage 4:

Back 69

1) Light energy is absorbed by PS1, which excites the electrons again to an even higher energy level.
2) Finally, the electrons are transferred to NADP, along with a proton from the stroma, to form reduced NADP.

Front 70

Cyclic Photophosphorylation:

Back 70

1) Cyclic photophosphorylation only uses PS1.
2) It's called cyclic because the electrons from the chlorophyll molecule aren't passed onto NADP, but are passed back to PS1 via electron carriers.
3) This means the electrons are recycled and can repeatedly flow through PS1.
4) This process doesn't produce any reduced NADP or 02 - it only produces small amounts of ATP.

Front 71

The Calvin Cycle:

Back 71

1) The Calvin Cycle takes place in the stroma of the chloroplasts.
2) It makes a molecule called TP from C02 and RuBP. TP can be used to make glucose and other organic substances.
3) There are a few steps in the cycle, and it needs ATP and H+ ions to keep it going.
4) The reactions are linked in a cycle, which means the starting compound, RuBP, is regenerated.

Front 72

The Three Stages of the Calvin Cycle:

Back 72

1) Carbon dioxide is combined with RuBP to form two molecules of GP.
2) ATP and reduced NADP are required for the reduction of GP to TP.
3) RuBP is regenerated.

Front 73

The Calvin Cycle - Stage 1:

Back 73

1) CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast.
2) Here, it's combined with RuBP, a 5-carbon compound. This gives an unstable 6-carbon compound, which quickly breaks down into two molecules of a 3-carbon compound called GP.
3) Rubisco catalyses the reaction between CO2 and RuBP.

Front 74

The Calvin Cycle - Stage 2:

Back 74

1) ATP from the light-dependent reaction provides energy to turn the 3-carbon compound GP into a different 3 carbon compound called TP.
2) This reaction also requires H+ ions, which come from reduced NADP. Reduced NADP is recycled to NADP.
3) TP is then converted into many useful organic compounds, e.g. glucose.

Front 75

The Calvin Cycle - Stage 3:

Back 75

1) Five out of every six molecules of TP produced in the cycle aren't used to make hexose sugars, but to regenerate RuBP.
2) Regenerating RuBP uses the rest of the ATP produced by the light-dependent reaction.

Front 76

TP and GP Conversion to Glucose:

Back 76

The Calvin Cycle is the starting point for making all the organic substances a plant needs, including carbohydrates, lipids and proteins:
1) Carbohydrates - glucose is made by joining two TP molecules together.
2) Lipids - made using glycerol, synthesised from TP.
3) Proteins - some amino acids are made from GP.

Front 77

6 Turns of the Calvin Cycle:

Back 77

1) The turns of the cycle produce 6 molecules of TP, because two molecules of TP are made for every one CO2 molecule used.
2) Five out of six of these TP molecules are used to regenerate RuBP.
3) For three turns of the cycle, only one TP is produced to make a hexose sugar.
4) A hexose sugar has six carbons, so two TP molecules are needed, meaning the cycle must turn 6 times to produce two molecules of TP for one hexose sugar.
5) 6 turns of the cycle need 18 ATP and 12 reduced NADP from the light dependent reaction.

Front 78

Optimum Light Intensity for Photosynthesis:

Back 78

1) Light is needed to provide the energy for the light-dependent reaction.
2) The higher the intensity of the light, the more energy it provides.
3) Only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments only absorb the red and blue light in sunlight. Plants look green because green light is reflected.

Front 79

Optimum Temperature for Photosynthesis:

Back 79

1) Photosynthesis involves enzymes (e.g. ATP synthase, rubisco). If the temperature falls below 10'C the enzymes become inactive, but if the temperature is more than 45'C they may start to denature.
2) At high temperatures stomata close to avoid losing too much water. This causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed.
3) The optimum temperature is around 25'C.

Front 80

Optimum Carbon Dioxide for Photosynthesis:

Back 80

1) Carbon dioxide makes up 0.04% of the gases in the atmosphere.
2) Increasing this to 0.4% gives a higher rater of photosynthesis, but any higher and the stomata start to close.

Front 81

Optimum Water for Photosynthesis:

Back 81

1) Plants also need a constant supply of water - too little and photosynthesis has to stop but too much and the soil becomes waterlogged (reducing the uptake of minerals such as magnesium, which is needed to make chlorophyll a).

Front 82

Photosynthesis - Limiting Factors:

Back 82

1) Light, temperature and CO2 can all limit photosynthesis if they are too low or too high.
2) On a warm, sunny, windless day, it's usually CO2 that's the limiting factor, and at night it's the light intensity.
3) However, any of these factors could become the limiting factor, depending on the environmental conditions.

Front 83

Commercial Growers on Photosynthesis:

Back 83

1) Commercial growers know the factors that limit photosynthesis and therefore limit plant growth.
2) They create an environment where plants get the right amount of everything that they need, which increases growth and so increases yield.
3) For example, CO2 is added to the air, light is provided 24 hours a day, and glasshouses trap heat energy, and a constant optimum temperature is maintained.

Front 84

The Four Stages of Aerobic Respiration:

Back 84

1) The four stages are: glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation.
2) The first three stages are a series of reactions. The products of these reactions are used in the final stage to produce loads of ATP.
3) The first stage happens in the cytoplasm of cells and the other 3 stages take place in the mitochondria.
4) All cells use glucose to respire, but organisms can also break down other complex organic molecules, which can then be respired.

Front 85

Aerobic Respiration Stage 1 - Glycolysis:

Back 85

1) Glycolysis involves splitting one molecule of glucose (6C) into two smaller molecules of pyruvate (3C).
2) The process happens in the cytoplasm of cells.
3) Glycolysis is the first stage of both aerobic and anaerobic respiration and doesn't need oxygen to take place - so it's an anaerobic process.

Front 86

Glycolysis Stage 1 - Phosphorylation:

Back 86

1) Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP.
2) This creates 2 molecules of TP and 2 molecules of ADP.

Front 87

Glycolysis Stage 2 - Oxidation:

Back 87

1) TP is oxidised (loses hydrogen), forming 2 molecules of pyruvate.
2) NAD collects the hydrogen ions, forming 2 reduced NAD.
3) 4 ATP are produced, but 2 were used up in stage 1, so there's a net gain of 2 ATP.

Front 88

Aerobic Respiration Stage 2 - The Link Reaction:

Back 88

1) Pyruvate is decarboxylated - one carbon atom is removed from pyruvate in the form of CO2.
2) NAD is reduced - it collects hydrogen from pyruvate, making acetate.
3) Acetate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA).
4) No ATP is produced in this reaction.

Front 89

The Link Reaction Happens Twice for every Glucose Molecule:

Back 89

1) Two pyruvate molecules are made for every glucose molecule that enters glycolysis. This means the link reaction and the Krebs cycle happen twice for every glucose molecule.

Front 90

Products of the Link Reaction:

Back 90

1) Two molecules of acetyl coenzyme A go into the Krebs cycle.
2) Two CO2 molecules are released as a waste product of respiration.
3) Two molecules of reduced NAD are formed and go to the last stage (oxidative phosphorylation).

Front 91

Anaerobic Respiration:

Back 91

1) In anaerobic respiration, pyruvate is converted into ethanol (in plants and yeast) and lactate (in animal cells and some bacteria).
2) The production of lactate or ethanol regenerates NAD. This means glycolysis can continue even when there isn't much oxygen around, so a small amount of ATP can still be produced to keep some biological processes going.

Front 92

Aerobic Respiration Stage 3 - The Krebs Cycle:

Back 92

1) The Krebs Cycle involves a series of oxidation-reduction reactions, which take place in the matrix of the mitochondria.
2) The cycle happens once for every pyruvate molecule, so it goes round twice for every glucose molecule.

Front 93

The Krebs Cycle - Stage 1:

Back 93

1) Acetyl CoA from the link reaction combines with oxaloacetate to form citrate.
2) Coenzyme A goes back to the link reaction to be used again.

Front 94

The Krebs Cycle - Stage 2:

Back 94

1) The 6C citrate molecule is converted to a 5C molecule.
2) Decarboxylation occurs, where CO2 is removed.
3) Dehydrogenation also occurs, where hydrogen is removed.
4) The hydrogen is used to produce reduced NAD from NAD.

Front 95

The Krebs Cycle - Stage 3:

Back 95

1) The 5C is then converted to a 4C molecule.
2) Decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two of reduced NAD.
3) ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP. When a phosphate group is directly transferred from one molecule to another it's called substrate-level phosphorylation. Citrate has now been converted into oxaloacetate.

Front 96

Products of the Krebs Cycle:

Back 96

1) 1 coenzyme A - Reused in next link reaction.
2) Oxaloacetate - Regenerated for next Krebs cycle.
3) 2 CO2 - Released as waste product.
4) 1 ATP - Used for energy.
5) 3 reduced NAD - To oxidative phosphorylation.
6) 1 reduced FAD - To oxidative phosphorylation.

Front 97

Aerobic Respiration Stage 4 - Oxidative Phosphorylation:

Back 97

1) Oxidative phosphorylation is the process where the energy carried by electrons, from reduced coenzymes is used to make ATP.
2) Oxidative phosphorylation involves two processes - the electron transport chain and chemiosmosis.

Front 98

Oxidative Phosphorylation - Stage 1:

Back 98

1) Hydrogen atoms are released from reduced NAD/FAD as they're oxidised to NAD/FAD. The H atoms split into protons and electrons.
2) The electrons move along the electron transport chain, losing energy at each carrier.
3) This energy is used to pump protons from the mitochondrial matrix into the intermembrane space.
4) Protons move down the electrochemical gradient, back into the mitochondrial matrix, via ATP synthase. This movement drives the synthesis of ATP from ADP + Pi.

Front 99

Oxidative Phosphorylation - Stage 2:

Back 99

1) The movement of H+ ions across a membrane, which generates ATP in stage 1 is called chemiosmosis.
2) In the mitochondrial matrix, at the end of the transport chain, the protons, electrons and oxygen (from the blood) combine to form water. Oxygen is the final electron acceptor.

Front 100

Total ATP Made From One Glucose Molecule:

Back 100

1) Glycolysis - 7 ATP
2) Link Reaction - 5 ATP
3) Krebs Cycle - 20 ATP
4) Total ATP - 32 ATP
5) All the ATP after glycolysis are synthesised during oxidative phosphorylation from coenzymes (reduced NAD and FAD).

Front 101

Energy Transfer Through Living Organisms:

Back 101

1) Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms, e.g. producers are eaten by organisms called primary consumers. Primary consumers are then eaten by secondary consumers, who are then eaten by tertiary consumers.
2) Each of the stages are called trophic levels.

Front 102

Food Chains and Webs:

Back 102

1) Food chains show simple lines of energy transfer.
2) Food webs show lots of food chains in an ecosystem and how they overlap.

Front 103

Energy Transfer Losses:

Back 103

1) Around 90% of the total available energy is lost in various ways.
2) Some of the available energy (60%) is never taken in by the organisms in the first place.
3) The rest of the energy is absorbed (40%), but 30% is lost to the environment through respiration.
4) 10% of the total energy available becomes biomass.

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Net Productivity:

Back 104

1) Net productivity = gross productivity - respiratory loss.
2) This means that the organisms must take its gross productivity (the 40% taken in) and then subtract its respiratory losses (the 30% lost by respiration) to get its net productivity (usually around 10% of total energy from sunlight or food, or 25% of gross productivity).

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Food Chains as Pyramid Diagrams:

Back 105

1) Food chains can be shown by drawing pyramids with each block representing a trophic level.
2) Producers are always on the bottom, then primary consumers are above them, followed by secondary consumers then tertiary consumers.
3) The area of each block tells you about the size of the trophic level.
4) There are three types of pyramid - pyramids of number, biomass and energy:

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Pyramids of Numbers:

Back 106

1) Pyramids of numbers show the number of organisms in each trophic level.
2) They're not always pyramid shaped though - small numbers of big organisms (like trees) or large numbers of small organisms (like parasites) change the shape.

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Pyramids of Biomass:

Back 107

1) Pyramids of biomass show the amount of biomass in each trophic level at a single moment in time.
2) They nearly always come out pyramid-shaped. An exception is when they're based on plant plankton - the amount of plant plankton is quite small at any given moment, but because they have a short life span and reproduce very quickly there's a lot around over a period of time.

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Pyramids of Energy:

Back 108

1) Pyramids of energy show the amount of energy available in each trophic level in kilojoules per square metre per year - the net productivity of each trophic level.
2) Pyramids of energy are always pyramid shaped.

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Natural Ecosystems:

Back 109

1) A natural ecosystem is an ecosystem that hasn't been changed by human activity.
2) The energy input of a natural ecosystem is the amount of sunlight captured by the producers in the ecosystem.

Front 110

Intensive Farming:

Back 110

1) Intensive farming involves changing an ecosystem by controlling the biotic or abiotic conditions to make it more favourable for crops or livestock.
2) This means intensively farmed crops or livestock can have greater net productivity than organisms in natural ecosystems.
3) The energy input might be greater in an intensively farmed area than in a natural ecosystem, or it might be the same.

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Intensive Farming Increases Productivity:

Back 111

1) They can increase the efficiency of energy conversion - more of the energy organisms have is used for growth and less is used for other activities.
2) They can remove growth limiting factors - more of the energy available can be efficiently used.
3) They can increase energy input - more energy is added to the ecosystem so there's more energy for growth.

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Killing Pest Species:

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1) Pests are organisms that reduce the productivity of crops by reducing the amount of energy available for growth.
2) This means the crops are less efficient at converting energy.
3) There are three ways that farmers reduce pest numbers: chemical pesticides, biological agents and integrated systems.

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Killing Pests - Chemical Pesticides:

Back 113

1) Herbicides kill weeks that compete with agricultural crops for energy, so crops receive more energy, and they grow faster and become larger.
2) Fungicides kill fungal infections that damage agricultural crops, so they grow faster and become larger.
3) Insecticides kill insect pests that eat and damage crops, so less biomass is lost from crops, and they grow larger, increasing productivity.

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Chemical Pesticides - Environmental Issues:

Back 114

1) They may directly affect (damage or kill) other non-pest species, e.g. butterflies.
2) They may indirectly affect other non-pest species, e.g. eating a lot of primary consumers that each contain a small amount of chemical pesticide can be enough to poison a secondary consumer.

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Chemical Pesticides - Economic Issues:

Back 115

1) Chemical pesticides can be expensive. It may not be profitable for some farmers to use chemical pesticides - their cost may be greater than the extra money made from increased productivity.

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Killing Pests - Biological Agents:

Back 116

1) Natural predators introduced to the ecosystem eat the pest species, e.g. ladybirds eat greenfly.
2) Parasites live in or lay their eggs on a pest insect. Parasites either kill the insect or reduce its ability to function.
3) Pathogenic bacteria and viruses are used to kill pests.

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Biological Agents - Environmental Issues:

Back 117

1) Natural predators introduced to an ecosystem may become a pest species themselves.
2) Biological agents can affect (damage or kill) other non-pest species.

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Biological Agents - Economic Issues:

Back 118

1) Biological agents may be less cost-effective than chemical pesticides, i.e. they may increase productivity less in the short term for the same amount of money invested.

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Killing Pests - Integrated Systems:

Back 119

1) Integrated systems use both chemical pesticides and biological agents.
2) The combined effect of using both can reduce pest numbers even more than either method alone, further increasing productivity.
3) Integrated systems can reduce costs if one method is particularly expensive - the expensive method can be used less because the two methods are used together.
4) They can reduce the environmental impact of things like pesticides, because less is used.

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Fertilisers:

Back 120

1) Fertilisers are chemicals that provide crops with minerals needed for growth, e.g. nitrates.
2) Crops use up minerals in the soil as they grow, so their growth is limited when there aren't enough minerals.
3) Adding fertilisers replaces the lost minerals, so more energy from the ecosystem can be used to grow, increasing the efficiency of energy conversion.

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Natural Fertilisers:

Back 121

1) Natural fertilisers are organic matter - they include manure and sewage sludge.

Front 122

Artificial Fertilisers:

Back 122

1) Artificial fertilisers are inorganic - they contain pure chemicals (e.g. ammonium nitrate) as powders or pellets.

Front 123

Fertilisers - Environmental Issues:

Back 123

1) Fertiliser can be washed into rivers and ponds, killing fish and plant life because of the eutrophication.
2) Using fertilisers changes the balance of nutrients in the soil - too much of a particular nutrient can cause crops and other plants to die.

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Fertilisers - Economic Issues:

Back 124

1) Farmers need to get the amount of fertiliser they apply just right. Too much and money is wasted as excess fertiliser is washed away (causing eutrophication). Too little and productivity won't be increased, so less money can be made from selling the crop.

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Rearing Livestock Intensively:

Back 125

1) This involves controlling the conditions they live in, so more of their energy is used for growth and less is used for other activities - the efficiency is increased so more biomass is produced, increasing productivity.
2) Animals may be kept in warm, indoor pens where their movement is restricted, so less energy is wasted.
3) Animals may be given feed that's higher in energy than their natural food, so more energy is available for growth.

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Costs and Benefits of Rearing Livestock Intensively:

Back 126

1) The benefits are that more food can be produced in a shorter space of time, often at lower cost.
2) However, enhancing productivity by intensive rearing raises ethical issues. For example, some people think the conditions intensively reared animals are kept in cause the animal pain, distress or restricts their natural behaviour, so it shouldn't be done.

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What is the Carbon Cycle:

Back 127

1) All organisms need carbon to make essential compounds, e.g. plants use CO2 in photosynthesis to make glucose.
2) The carbon cycle is how carbon moves through living organisms and the non-living environment.
3) It involves four processes - photosynthesis, respiration, decomposition and combustion.

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The Carbon Cycle:

Back 128

1) Carbon (in the form of CO2) is absorbed by plants when they carry out photosynthesis - it becomes carbon compounds in plant tissues.
2) It is passed on through the trophic levels through consumption.
3) All living organisms die and the carbon compounds are digested by microorganisms called decomposers. This is called saprobiontic nutrition.
4) Carbon is returned to the air and water as all living organisms carry out respiration, producing CO2.
5) Without decomposers, carbon compounds can be turned into fossil fuels over millions of years by heat and pressure.
6) The carbon in fossil fuels is released during combustion.

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CO2 Concentration Fluctuations:

Back 129

1) Respiration adds CO2 to the atmosphere. Photosynthesis removes CO2 from the atmosphere.
2) The amount of respiration and photosynthesis going on varies on a daily and a yearly basis, so the amount of atmospheric CO2 changes.

Front 130

Daily Change in CO2 Concentration:

Back 130

1) Respiration is carried out constantly through the day and night, whereas photosynthesis only takes place during the daylight hours.
2) CO2 concentration falls during the day because it's being removed by plants through photosynthesis.
3) CO2 concentration increases at night because it's no longer being removed, but all organisms are still respiring and adding CO2 to the atmosphere.

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Yearly Change in CO2 Concentration:

Back 131

1) Most plant life exists in the northern hemisphere because that's where most land is.
2) Most plant growth occurs in the summer because that's when the light intensity is greatest.
3) CO2 concentration falls during sumer because more is being removed from the atmosphere as more plants are photosynthesising.
4) CO2 concentration increases throughout the winter and autumn because less is being removed from the atmosphere, as fewer plants are photosynthesising.

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Global Warming:

Back 132

1) Global warming is the increase in average global temperature over the last century.
2) Many scientists think the rate of increase is unprecedented - mostly caused by human activity.
3) It's thought human activity has caused global warming by enhancing the greenhouse effect - the effect of greenhouse gases absorbing outgoing energy, so that less is lost to space.
4) The greenhouse effect is essential to keep the planet warm, but too much and the planet warms up.
5) Two of the main greenhouse gases are CO2 and methane.

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Greenhouse Gases - Carbon Dioxide:

Back 133

1) Atmospheric CO2 concentration has increased rapidly since the mid-19th century from 280 ppm to nearly 380 ppm. The concentration has been stable for the previous 10000 years.
2) It is increasing as more fossil fuels are burnt.
3) It is also increased by the destruction of natural sinks. E.g. trees are a big CO2 sink - they store the carbon as organic compounds. CO2 is released when trees are burnt, or when decomposers break down the organic compounds and respire.

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Greenhouse Gases - Methane:

Back 134

1) Atmospheric methane concentration has increased rapidly since the mid-19th century from 700ppb to 1700 ppb in 2000. The level had been stable for the previous 850 years.
2) It is increasing because more methane is being released into the atmosphere, e.g because more fossil fuels are being extracted, more decaying waste and more cattle giving it off as a waste gas etc.
3) Methane can also be released from natural stores, e.g. frozen ground. As temperatures increase, it's thought these stores will thaw and release large amounts of methane into the atmosphere.

Front 135

Global Warming on Crop Yield:

Back 135

1) The increasing CO2 concentration that's linked to global warming could also be causing an increase in crop yields.
2) CO2 concentration is a limiting factor for photosynthesis, so increasing global CO2 concentration could mean crops grow faster, increasing crop yields.

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Global Warming on Insect Pests:

Back 136

1) Climate change may affect the life cycle of some insects. For example, some insects may go through their larval stage quicker and emerge as adults earlier
2) Climate change is also making some species more abundant, e.g. warmer and wetter summers in some places have led to an increase in mosquito numbers.
3) Other species may become less abundant, e.g. some tropical insects can only thrive in specific temperature ranges, so if it gets too hot, fewer insects will be able to reproduce successfully.

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Global Warming on Wild Animals and Plants:

Back 137

1) Climate change could affect the distribution of many wild animal and plant species, depending on how they survive in certain temperatures.
2) Climate change could also affect the number of wild animals and plants, e.g. boarfish are increasing in number in parts of the Atlantic Ocean where sea temperature is rising, yet polar bears are becoming less abundant due to the lack of sea ice.

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The Nitrogen Cycle:

Back 138

1) Plants and animals need nitrogen to make proteins and nucleic acids. The atmosphere's made up of around 78% nitrogen, but plants and animals can't use it in that form - they need bacteria to convert it into nitrogen compounds first.
2) The nitrogen cycle shows how nitrogen is converted into a useable form and then passed on between different living organisms and the environment.
3) The four stages of the nitrogen cycle are - nitrogen fixation, ammonification, nitrification and denitrification.

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Nitrogen Cycle Stage 1 - Nitrogen Fixation:

Back 139

1) Nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by bacteria. The ammonia can then be used by plants.
2) The bacteria are found inside root nodules.
3) They form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the plant provides them with carbohydrates.

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Nitrogen Cycle Stage 2 - Ammonification:

Back 140

1) Ammonification is when nitrogen compounds from dead organisms are turned into ammonium compounds by decomposers.
2) Animal waste also contains nitrogen compounds. These are also turned into ammonium compounds by decomposers.

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Nitrogen Cycle Stage 3 - Nitrification:

Back 141

1) Nitrification is when ammonium compounds in the soil are changed into nitrogen compounds that can be used by plants.
2) First nitrifying bacteria change ammonium compounds into nitrites.
3) Then other nitrifying bacteria change nitrites into nitrates.

Front 142

Nitrogen Cycle Stage 4 - Denitrification:

Back 142

1) Denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce nitrogen gas.
2) This happens under anaerobic conditions, e.g. in waterlogged soils.

Front 143

The Haber Process:

Back 143

1) Parts of the nitrogen cycle can also be carried out artificially and on an industrial scale.
2) The Haber Process produces ammonia from atmospheric nitrogen - it's used to make things like fertilisers.

Front 144

Leaching:

Back 144

1) Leaching is when water-soluble compounds in the soil are washed away, e.g. by rain or irrigation systems. They're often washed into nearby ponds and rivers.
2) If nitrogen fertiliser is leached into waterways it can cause eutrophication.

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Eutrophication:

Back 145

1) Nitrates leached from fertilised fields stimulate the growth of algae in ponds and rivers.
2) Large amounts of algae block light from reaching the plants below.
3) Eventually the plants die because they're unable to photosynthesise enough.
4) Bacteria feed on the dead plant matter.
5) The increased numbers of bacteria reduce the oxygen concentration through aerobic respiration.
6) Fish and other aquatic organisms die because there isn't enough dissolved oxygen in the water.

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Succession:

Back 146

1) Succession is the process by which an ecosystem changes over time.
2) The biotic conditions change as the abiotic conditions change.
3) There are two types of succession: Primary and secondary.

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Primary Succession:

Back 147

1) Primary succession - this happens on land that's been newly formed or exposed, e.g. where a volcano has erupted to form a new rock surface, or where sea level has dropped exposing a new area of land.
2) There's no soil or organic material to start with, e.g. just bare rock.

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Secondary Succession:

Back 148

1) Secondary succession - this happens on land that's been cleared of all the plants, but where the soil remains, e.g. after a forest fire or where a forest has been cut down by humans.

Front 149

Succession Phase 1 (Pioneer Species):

Back 149

1) Seeds and spores are blown in by the wind and begin to grow. The first species to colonise the area are called pioneer species.
2) The abiotic conditions are hostile, and only pioneer species grow because they're specialised to cope with the harsh conditions.
3) The pioneer species change the abiotic conditions - they die and microorganisms decompose the dead organic material (humus). This forms a basic soil, making conditions less hostile, and allowing other plants such as shrubs to grow.

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Succession Phase 2:

Back 150

1) At each stage of succession, different plants and animals that are better adapted for the improved conditions move in, out compete the plants and animals that are already there, and become the dominant species in the ecosystem.
2) As succession progresses, the ecosystem becomes more complex. New species move in alongside existing species which increases the species diversity.

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Succession Phase 3 (Climax Community):

Back 151

1) The final stage of succession is called the climax community - the ecosystem is supporting the largest and most complex community of plants and animals it can. It won't change much more - it's in a steady state.

Front 152

Climatic Climax:

Back 152

1) Which species make up the climax community depends on what the climate's like in an ecosystem.
2) For example, in a temperate climate there's plenty of water, mild temperatures and not much change between seasons. The climatic climax will contain large trees because they can grow in these conditions once deep soils have developed. However, large trees would not be apart of the climax community in a polar climate.

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Plagioclimax:

Back 153

1) Human activities can prevent succession, stopping a climax community from developing. When succession stopped artificially like this the climax community is called a plagioclimax.

Front 154

Conservation:

Back 154

1) Conservation sometimes involves preventing succession in order to preserve an ecosystem in its current seral stage, e.g. moorland in Scotland.

Front 155

Managing Succession for Conservation:

Back 155

1) Animals are allowed to graze on the land. This is similar to mowing - the animals eat the growing points of the shrubs and trees, which stops them from establishing themselves and helps to keep vegetation low.
2) Managed fires are lit. After the fires, secondary succession will occur on the moorland - the species that grow back first are the species that are being conserved, e.g. heather. Larger species take longer to grow back and will be removed again the next time the moor's burnt.

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Importance of Conservation:

Back 156

1) Species are resources for lots of things that humans need, e.g. potential drugs, clothes and food.
2) Some people think it's the ethical choice to make.
3) Many species/habitats are aesthetically pleasing.
4) Conserving species/habitats can help to prevent climate change.
5) It helps to prevent the disruption of food chains, which could result in the loss of resources.

Front 157

Plant Conservation - Seedbanks:

Back 157

1) A seedbank is a store of lots of seeds from lots of different plant species.
2) They help to conserve endangered plants as well as different varieties of each species (tall/short etc).
3) Large numbers of species can be conserved as seeds don't need much space and they can be stored anywhere for a long time, as long as it's cool and dry.
4) However, seeds must be regularly tested to see if they're still viable, which can be expensive and time-consuming.

Front 158

Fish Conservation - Fishing Quotas:

Back 158

1) These are limits to the amount of certain fish species that fisherman are allowed to catch.
2) International agreements are made that state the amount of fish each country can take, and where from
3) This reduces the number of fish caught and killed, so populations aren't reduced too much and the species aren't at risk of becoming extinct.
4) However, many fisherman don't agree with the scientists, and they also cause job losses.

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Animal Conservation - Captive Breeding Programmes:

Back 159

1) This involves breeding animals, usually endangered species, in controlled environments, e.g. pandas.
2) However, animals can have problems breeding outside their natural habitat.
3) Animals bred in captivity can be reintroduced to the wild, however, this can cause problems like bringing new diseases to habitats and harming other species in the ecosystem.

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Conservation - Relocation:

Back 160

1) Relocating a species means moving a population of a species to a new location if they're under threat.
2) The species are moved to a similar area where they're not at risk.
3) It's often used for species that only exist in once place, and it's aim is to increase the species' numbers.
4) However, this can cause problems, as native species may be outcompeted and become endangered themselves.

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Habitat Conservation - Protected Areas:

Back 161

1) Protected areas such as national parks and nature reserves protect habitats by restricting urban development, industrial development and farming.
2) Habitats in protected areas can be managed to conserve them.
3) However, national parks are also used as tourist destinations, meaning there's conflict between the need to conserve and the need to allow people to visit and use them.

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Gene:

Back 162

1) A sequence of bases on a DNA molecule that codes for a protein (polypeptide), which results in a characteristic, e.g. the gene for eye colour.

Front 163

Allele:

Back 163

1) A different version of a gene. Most plants and animals have two alleles of each gene, one from each parent.
2) The order of bases in each allele is slightly different - they code for different versions of the same characteristic, and they're represented using letters, e.g. Bb.

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Genotype:

Back 164

1) The genetic constitution of an organism - the alleles an organism has, e.g. BB, Bb or bb for eye colour.

Front 165

Phenotype:

Back 165

1) The expression of the genetic constitution and its interaction with the environment - an organisms characteristics, e.g. brown eyes.

Front 166

Dominant:

Back 166

1) An allele whose characteristic appears in the phenotype even when there's only one copy.
2) Dominant alleles are shown by a capital letter.

Front 167

Recessive:

Back 167

1) An allele whose characteristic only appears in the phenotype if two copies are present.
2) Recessive alleles are shown by a lower case letter.

Front 168

Codominant:

Back 168

1) Alleles that are both expressed in the phenotype - neither one is recessive, e.g. the alleles for haemoglobin.

Front 169

Locus:

Back 169

1) The fixed position of a gene on a chromosome.
2) Alleles of a gene are found at the same locus on each chromosome in a pair.

Front 170

Homozygote:

Back 170

1) An organism that carries two copies of the same allele, e.g. BB or bb.

Front 171

Heterozygote:

Back 171

1) An organism that carries two different alleles, e.g. Bb.

Front 172

Punnett Square:

Back 172

1) A Punnett square is just another way of showing a genetic diagram - they're also used to predict the genotypes and phenotypes of offspring.

Front 173

Sex-Linked Characteristics:

Back 173

1) In mammals, females are XX and males are XY.
2) Genes on sex chromosomes are said to be sex-linked because the chance of an individual inheriting them is affected by their gender.
3) The Y chromosome is smaller than the X chromosome and carries fewer genes. So most genes on the sex chromosomes are only carried on the X chromosome.
4) As males have only one X chromosome, they are more likely than females to show recessive phenotypes for genes that are sex-linked.
5) Genetic disorders inherited this way include colour blindness and haemophilia - both carried on the X chromosome (X-linked disorders).

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Colour Blindness - Sex-Linked Disorder:

Back 174

1) Colour blindness is a sex-linked disorder carried on the X chromosome. As it's sex-linked both the chromosome and the allele are represented in the genetic diagram.
2) Females would need two copies of the recessive allele to be colour blind, while males only need one copy. This means colour blindness is much rarer in women than men.

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Multiple Alleles:

Back 175

1) Inheritance is more complicated when there are more than two alleles of the same gene.
2) In the ABO blood group system in humans there are three alleles for blood type.

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Shared Gene Pool:

Back 176

1) A species is defined as a group of similar organisms that can reproduce to give fertile offspring.
2) A population is a group of organisms of the same species living in a particular area.
3) Species can exist as one or more populations.
4) The gene pool is the complete range of alleles present in a population.
5) How often an allele occurs in a population is called the allele frequency. Its usually given as a percentage of the total population, e.g. 35%

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The Hardy-Weinberg Principle:

Back 177

1) The Hardy-Weinberg principle predicts that the frequencies of alleles in a population won't change from one generation to the next.
2) This is only true under certain conditions - it has to be a large population where there's no immigration, emigration, mutations or natural selection, as well as random mating.

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The Hardy-Weinberg Principle - Predicting Allele Frequency:

Back 178

1) You can figure out the allele frequency of one allele if you know the frequency of the other using this equation: p+q=1
p = the frequency of the dominant allele
q = the frequency of the recessive allele
2) E.g. a species of plant has either red or white flowers. R is dominant and r is recessive. If the frequency of R is 0.4, then the frequency of r is 0.6.

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The Hardy-Weinberg Principle - Predicting Genotype Frequency:

Back 179

1) You can figure out the frequency of one genotype if you know the frequencies of the others, using this equation: p(squared) + 2pq + q(squared) = 1
p(squared) = the frequency of the homozygous dominant genotype
q(squared) = same but recessive
2pq = the frequency of the heterozygous genotype
2) E.g. if there are two alleles for flower colour (R and r), there are three possible genotypes (RR, Rr, rr). If the frequency of RR is 0.34 an the frequency of Rr is 0.27, then the frequency of rr must be 0.39.

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Differential Reproductive Success:

Back 180

1) Not all individuals are as likely to reproduce as each other. There's differential reproductive success in a population - individuals with an allele increasing their chance of survival are more likely to reproduce and pass on their genes, meaning a greater proportion of the next generation inherit the beneficial allele, increasing the frequency of the beneficial allele from generation to generation.
2) This process is called natural selection.

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Stabilising Selection:

Back 181

1) Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
2) This occurs when the environment isn't changing, and it reduces the range of possible phenotypes.

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Directional Selection:

Back 182

1) Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
2) This could be in response to an environmental change.
3) It causes genetic change in the population.

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Speciation:

Back 183

1) This is the development of a new species, and it occurs when populations of the same species become reproductively isolated - geographical isolation.
2) The populations will experience slightly different conditions, e.g. different climates.
3) Selective pressures will impact on allele frequencies, and mutations will occur independently in each population.
4) The changes in allele frequency will lead to differences accumulating in the gene pools, causing changes in phenotype frequencies.
5) Eventually the separated populations won't be able to breed together to produce fertile offspring - they'll have become reproductively isolated and they will now be separate species.