AS AQA Biology Unit 2


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what is independent segregation?

= When the gametes are produced, different combinations of matneral and paternal chromosomes go into each cell.

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What does the enzyme DNA Polymerase do in DNA repl

= DNA Polymerase joins the nucleotides together and hydrodgen bonds form between the strands.

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What does the enzyme DNA Helicase do in DNA replic

= The enzyme DNA Helicase breaks the hydrodgen bonds between the two polynucleotide DNA strands. The helix unzips to form two single strands.

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What are the two main uses of mitosis?

= Growth and repair of damaged tissues.

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Name the four stages of mitosis

= 1. Prophase- The chromosomes condense and shorten.

2. Metaphase - Chromosomes line up at equator of the cell.

3. Anaphase- Chromatids seperate.

4. Telophase- Nuclear envelope forms again.

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Gases are exchanged in plants through the stomata.

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Spiracles are pores on an insect's body surface which air moves through.

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What are the advantages of the counter-current sys

It maintains a large concentration gradient between the water and the blood,so as much oxygen as possible can diffuse from the water into the blood.

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How are single-celled organisms adapted for gas ex

= They have a relatively large surface area, a thin flat surface and a short diffusion pathway.

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DNA replication is described as semi conservative because half of the new strands of DNA are from the original piece of DNA.

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A tissue is a collection of similar cells that are suited to the same function.

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The process by which cells adapt themselves to suit a specific function is called cell differentiation.

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Cancer chemical drugs (or chemotherapy) work by preventing the synthesis of enzymes needed for DNA repication,therfore the cell cycle is disrupted and the cell dies.

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Haemoglobin is a protein with a quaternary structure because it is made up of four polypeptide chains.

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The bonds that join sugars together are glycosidic bonds.

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Genetic diversity is caused by differences in alleles.

More alleles=more diversity.

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Which bases join together in a DNA molecule?

Adenine to Thymine and Cytosine to Guanine

(At The Golf Couse)

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In a DNA molecule the bases are joined together by hydrodgen bonds.

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The three main components of nucleotides are : Phosphate, deoxyribose sugar and base.

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Genes are sections of DNA found on chromosomes that code for proteins.

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Intraspecific variation = the differences that occur within a species

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The founder effect describes what happens when just a few organisms from a population start a new colony. Only a small number of organisms have contributed their alleles to the gene pool, so there will be less variation.

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Standard deviation tells you how much the values in a single sample vary. It's a measure of the spread of values about the mean. More similar values means a smaller standard deviation.

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DNA is tightly coiled so that a lot of genetic information can fit into a small space in the cell nucleus.

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Oxygen dissociation curve to the right = organisms that have a high respiratory rate have a lower affinity for oxygen so that oxygen dissociates into the muscles more easily.

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genetic diversity is increased by mutations in the DNA and different alleles being introduced by migration.

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interspecific variation is the variation that exists between different species.

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Variation can be caused by genetic and environmental factors.

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Scientists only look at a sample population because to measure a whole population would be too difficult and time-consuming.

A population sample should be chosen at random to reduce the effects of bias and chance.

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A large surface area to volume ratio increases heat loss whereas a smaller ratio reduces heat loss.

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Cancer is a tumour that invades surrounding tissue.

Mutation in a gene that controls cell division means that cells can't stop dividing. All these extra cells form a tumour.

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One haemoglobin molecule can carry up to four oxygen molecules.

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A DNA triplet is the sequence of three bases that code for an amino acid in a gene.

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Monosaccharides are joined together by condensation reactions.

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An allele is a different form of a particular gene.

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Mutations are changes in the base sequence of an organism's DNA.

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Selective breeding involves humans selecting which organisms reproduce together in order to produce high yielding breeds.

It can be used to produce animals and plants that are resistant to disease so fewer drugs and pesticides are needed.

However it reduces genetic diversity which increases the incidence of genetic diseases.

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organisms that live in environments with a low partial pressure of oxyen need to have a higher affinity for oxygen.

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a haploid cell (a gamete) has only one copy of each chromosome. a diplod cell has both copies.

meiosis produces four haploid cells that are genetically different from each other.

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the bohr effect = when cells respire they produce carbon dioxide. this increases the rate of oxygen loading so the curve shifts to the right.

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plants store excess glucose as starch. it is a MIXTURE of two polysaccharides of alpha glucose and is insoluble in water. this means that water cannot enter by osmosis and cause swelling.

the coiled structure of amylose makes starch compact so you can fit more in.

branches of amylopectin = larger surface area = glycosidic bonds can be broken more easily = glucose is released more quickly.

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cellulose is made of long unbranched chains of beta glucose.

the chains are parallel.

the cellulose chains are linked together by hydrodgen bonds to form strong fibres which provide structural support.

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during meiosis,homologus chromosomes pair up.

the chromatids twist around each other and bits swap over.

they have the same genes but different alleles.

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Really useful. Thanks



these were really helpful notes! thankyou! :)

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