Biology Revision B6

Front 1

Plant sex cells

Back 1

Stamens: The male parts of the flower (each consists of an anther held up on a filament)

Anthers: Produce male sex cells (pollen grains)

Stigma: The top of the female part of the flower which collects pollen grains

Ovary: Produces the female sex cells (contained in the ovules)

Front 2

Animal sex cells

Back 2

Sperm and egg

Front 3

Meiosis

Back 3

In the gamete mother cell, before meiosis begins, each chromosome replicates.

At this stage each chromosome exists as two genetically identicalchromatids attached to their centromere. This shows four chromosomes within the nucleus of the cell. Each chromosome appears as two chromatids attached to a centrometre.

In the first meiotic division chromosomes align in homologous pairs. Points of contact form between members of the same homologous pair. The shaded chromosomes are identical to those that were originally donated by one of the parents in the ovum. The white chromosomes are identical to those that were originally donated from the other parent in the sperm that fertilised the ovum. The points of contact or crossing over between members of a homologous pair are the chiasmata.

The homologous pairs move to the equator of the cell. Equal lengths of the chromatids of the same homologous pair have broken off and crossed over. The chromosomes align at random and independantly. Only one possible arrangement is shown.

Homologous pairs align at random at the equator of the cell. This shows the early separation of the chromosomes of each of the homologous pairs.

Homologous pairs are separated. This shows the cell at an early stage of meiotic division. The cell membrane is starting to pinch inwards.

The cell divides to form two cells each with a haploid set of chromosomes. Cell division is complete and two cells containing a haploid set of chromosomes are formed.

In the second meiotic division the chromosomes in each cell align independently and randomly at the equator of the cell.

The chromatids in each cell are separated. The chromatids are pulled towards the opposite poles of the cell.

The cells divide. The cell membrane is starting to pinch inwards.

Cell division is complete, resulting in the formation of four cells each with the haploid number.

Front 4

Mitosis

Back 4

1.parent cell

2.chromosomes make identical copies of themselves

3.they line up along the centre

4.they move apart

5.two daughter cells form with identical chromosomes to the parent cell

Front 5

Genome

Back 5

A genome is an organism's complete set of DNA

Front 6

Base pairs of DNA

Back 6

A-T

C-G

Front 7

How protein structure is determined by the DNA base code

Back 7

Proteins are made from lots of amino acids joined together. Each amino acid is coded by the sequence (order) of three bases. For example, GGT codes are found in glycine but TCA codes are found in serine, a different amino acid. The sequence of bases determines the sequence of amino acids in a protein molecule.

Front 8

Messenger RNA (mRNA)

Back 8

The genetic code needed to make a particular protein is carried from the DNA to the ribosomes by a molecule called mRNA

Front 9

The Synthesis of Proteins in the ribosomes

Back 9

The ribosomes are the sites of protein synthesis

the mRNA strand attaches to a ribosome

tRNA molecules transport specific amino acids to the ribosome

each mRNA codon codes for a specific amino acid

the anti-codons and codons match up and form complementary base pairs

peptide bonds form between the adjacent amino acids to form the polypeptide (protein)

Front 10

Dna Mutations

Back 10

They occur continuously but most don't change the protein synthesized by the gene

Front 11

Switching on and off genes

Back 11

Not all genes code for proteins and some turn on and off other genes

Front 12

Genotype and phenotype

Back 12

PHENOTYPE is the physical appearance resulting from the inherited information. e.g. someone with blue eyes has the phenotype blue eyes.

Genotype is the alleles (Bb)

Front 13

homozygous and heterozygous

Back 13

An organism can be homozygous dominant, if it carries two copies of the same dominant allele, or homozygous recessive

Front 14

Inherited diseases

Back 14

Recessive

Cystic Fibrosis

Dominant

Huntingdon's disorder

Front 15

A GM Crop

Back 15

A GM cop is a crop that has been genetically modified.

E.g. golden rice that contain beta carotene to combat vitamin A dificiency

or crops that are resistant to herbicides

Front 16

Disadvantages of gm crops

Back 16

There are concerns that food from GM plants might harm peopleseed for GM plants can be expensive

Front 17

Cloning by plant cuttings and tissue culture

Back 17

Cuttings

The simplest way to clone a plant involves taking a cutting. A branch from the parent plant is cut off, its lower leaves removed and the stem planted in damp compost. Plant hormones are often used to encourage new roots to develop. The cutting is usually covered in a clear plastic bag at this stage to keep it moist and warm. After a few weeks, new roots develop and a new plant is produced. The method is easy enough for most gardeners to do successfully.

Tissue culture

Another way of cloning plants is by tissue culture, which works not with cuttings but with tiny pieces from the parent plant. Sterile agar jelly with plant hormones and lots of nutrients is needed. This makes tissue culture more expensive and difficult to do than taking cuttings.

Front 18

Lamarks theory

Back 18

Jean-Baptiste Lamarck was a French scientist who developed an alternative theory of evolution at the beginning of the 19th century. His theory involved two ideas:

A characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears

Any feature of an organism that is improved through use is passed to its offspring.

Front 19

Alfred russel wallace

Back 19

He did a lot of research and his researched helped to prove Darwin's theories

Front 20

History of genetics

Back 20

Mid 19th century Mendel carried out breeding experiments on plants but people did not realise its significance until after his death

Late 19th century behavior of chromosomes during division was observed

The structure off DNAwas determined in the 20th century.

Front 21

Why there are no fossils of many early life forms

Back 21

Because many of the were soft bodied

Front 22

Carl Linnaeus

Back 22

He invented the Binomial system.

The five kingdoms are:

animals (all multicellular animals)

plants (all green plants)

fungi (moulds, mushrooms, yeast)

prokaryotes (bacteria, blue-green algae)

protoctists (Amoeba, Chlorella and Plasmodium)

Further divisions

Living things can then be ranked according to:

phylum

class

order

family

genus

species