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Biology paper 2 2022 AQA GCSE Separate science > Reproduction > Flashcards

Reproduction Flashcards

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1
Q

explain mitosis

A

in mitosis, one cell divides into two identical daughter cells

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2
Q

what are the two gametes in humans

A

sperm cells

egg cells

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3
Q

which cells are smaller, sperm cells or egg cells?

A

sperm cells are much smaller than egg cells

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4
Q

in gametes chromosomes are not paired, they are single so how many single chromosomes do gametes have

A

23 single chromosomes

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5
Q

what type of cell division are gametes made in?

A

meiosis

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6
Q

meiosis produces unidentical cells what does this mean

A

every sperm cell and every egg cell produced is different.

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7
Q

Aside from in animals. where else does meiosis take place and what are the gametes in this case?

A

meiosis also takes place in flowering plants

in this case the gametes are pollen and egg cells

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8
Q

what are the key features of sexual reproduction

A

sexual production involves the fertilisation of male and female gametes.
as both every sperm cell and every egg cell are different, in sexual production there is mixing of genetic information.
the offspring recieves genetic information from both male and female parents
there is variation in the offspring

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9
Q

what is an aphid reproducing an example of

A

-asexual reproduction

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10
Q

asexual reproduction in the context of an aphid

A

in asexual reproduction there is only one parent so the aphid is the only parent of the offspring.
asexual reproduction does not involve gametes
because there is only one parent, there is no mixing of the genetic information so the offspring are all gentically identical.
these offsprings are known as clones

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11
Q

because asexual reproduction does not involve gametes, meiosis does not take place. asexual reproduction involves mitosis only.

A

asexual reproduction- one parent involved
only one parent so no mixing of genetic information
offspring are all genetically identical
offsprings are clones

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12
Q

another example of asexual reproduction are buds

A

buds drop off and grow into new plants

offspring plants are genetically identical to the parent - they are clones

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13
Q

how many single chromsomes do human gametes contain

A

23 single chromosomes

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14
Q

key steps of meiosis

A

-meiosis only takes place in reproductive organs such as the ovaries (females) and the testes.(males)
first stage of meiosis, all of the chromosomes are copied
cell now divides into two
now both of these cells divide one more time forming the gametes.
in the gametes the chromosomes are now singled and not paired.
meiosis has halved the number of chromosomes
meiosis produces 4 gametes from one original cell
each of these 4 gametes are gentically different from one another.
each gamete has different alleles

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15
Q

in sexual reproduction

A

-gametes join together- scientists call this fertilisation ( when a female gamete and a male gamete fuse)
after fertilisation, cell now has full number of chromosomes.

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16
Q

human sperm cell and human egg cell both contain 23 single chromosomes each but when fertilised, they contain 23 chromosome pairs.
what happens after fertilisation

A

the new cell divides by mitosis, producing a clump of identical cells. scientists call this clump of identical cells an embryo.
as the embryo develops the cells diffrentiate forming differnet types of cells. (nerve cells and muscle cells in animals)

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17
Q

where are chromosomes found

A

in the nucleus of cells

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18
Q

chromosomes contain a molecule called DNA. why do scientists say that DNA is our genetic material

A

that is because DNA determines are inherited features.

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19
Q

DNA consists of two strands what are these strands called

A

polymer chains

in dna the two strands wrap around each other to form a double helix.

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20
Q

what is the defintion of a gene

A

a gene is a small section of DNA on a chromosome.

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21
Q

proteins are made by joining together amino acids. each gene encodes for a specific sequence of amino acids to make a specific…

A

proteins are made by joining together amino acids. each gene encodes for a specific sequence of amino acids to make a specific protien.

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22
Q

blood type gene example

A

blood type gene encodes the sequence of amino acids for the protein that determines blood type.

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23
Q

humans have thousands of genes. do both chromsomes in a pair have the same genes or different genes.

A

both chromosomes in a pair have the same genes.

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24
Q

what is the definition of a genome

A

the genome is the entire genetic material of an organism. the human genome is the entire genetic material that makes a human.

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25
Q

what are some of the benefits of scientists studying the entire human genome?

A
  • understanding the entire genome can help us search for genes that are linked to diseases. e.g genes that increase the risk of developing cancer or alzheimars disease.
  • understanding the human genome will help us understand and treat inherited disorders such as cystic fibrosis.
  • to trace human migration patterns from the past ( this helps people to discover their ancestory)
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26
Q 
DNA STRUCTURE (triple biology) 
 recap of DNA
A
  • DNA is the genetic material
  • DNA is contained in chromosomes in the nucleus.
  • DNA is a polymer made up of two strands. the two strands wind around each other to form a double helix.
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27
Q

DNA is a polymer of molecules called nucleotides what is the structure of a nucleotide?

A 
three main parts
- a phosphate group
- a sugar molecule
- a base
circle is the phosphate group
pentagon is the sugar molecule
rectangle is the base
28
Q

what never changes in the structure of nucleotides in DNA

A

In DNA, the phosphate group and sugar molecule never change

29
Q

there are 4 bases name them

A

-Adenine
-Cytosine
-Guanine
-Thymine
this means DNA contains 4 different nucleotides.

30
Q

DNA strands are…..

A

complimentary
the same bases always pair on the oppsite strands
C is always linked to G
A is always linked to T

31
Q

why do we say that the two strands are complimentary

A

because the same bases always pair on the two strands.

32
Q

the basics that we need to understand of protein synthesis

A

there are 4 different nucleotides, each nucleotide has a different base (A,T,C,G)
the two strands are complimentary as A always pairs with T on opposite strands and C always pairs with G on oppsite strands)

33
Q

proteins are polymers of amino acids

A

most proteins contain hundreds of amino acids joined together
there are 20 different amino acids in humans

34
Q

how many different amino acids are there in humans

A

20

35
Q

describe stages of protein synthesis:

could be a difficult question in the exam

A

there are two main stages: transcription and translation
first stage- happens in the nucleus - transcription
base triplet is copied onto a complementary template molecule also known as mrna

36
Q

two different proteins both have a different order of amino acids. what does the specific order of the amino acids determine

A

the specific order of amino acids determines the shape of the protein. the shape of protein determines its function.

37
Q

the order of the amino acids in the protein determines its shape and its function.
what is the specific order of amino acids in the protein determined by

A

the order of amino acids in the protein is determined by the sequence of bases in the gene for that protein.

38
Q

below is a short stretch of a gene. this only shows one of the other strands of DNA, the other strand is complimentary to this one
ATG GGA CGC ATA TAC TTT

A

the cell reads the DNA sequence as a triplet of bases. each triplet encodes for a specific amino acid in the protein.
(complimentary strand to one above) TAC CCT GCG TAT ATG AAA

39
Q

there are two main stages of protein synthesis what are they?

A

first stage takes place in the nucleus and second stage takes place in the cytoplasm.
the first stage is called transcription ( transcription takes place in the nucleus)
in this stage base sequence of the gene is copied onto a complementary template molecule. ( mrna messenger RNA)
mrna is single stranded molecule.
the complementary template molecule ( mrna) passes out of nucleus and into the cytoplasm.
second stage of protein synthesis is called translation. in this stage the mrna molecule ( complimentary template molecule) attaches onto a ribosome. amino acids are now brought to the ribosome on carrier molecules. carrier molecules are called trna ( transfer RNA). ribosome reads triplet of bases on mrna and uses this to join together correct amino acids in the correct order. once protein chain is complete it now folds into its unique shape and the shape enables the protein to do its job.

40
Q

what is called a mutation

A

a change to a base is called a mutation

41
Q

when do mutations happen

A

all the time

42
Q

a change to a base may not always change the sequence of amino acids why?

A

because different base sequences can sometimes code for the same amino acid so mutation in this case has no effect on protein’s shape or function.

43
Q

what happens if the change to a base sequence has altered the shape of the protein

A

protein now has a different amino acid, this has altered the shape of the protein. this mutation can effect function of a protein e.g active site of an enzyme may change shape so substrate can no longer fit.

44
Q

if a mutation changes the shape of a structural protein such as collagen , what could happen

A

it could lose strength.

45
Q

mutation in non coding parts of DNA

A

these no coding regions switch genes on and off. these regions tell genes when to produce proteins.mutations in these non coding regions can affect how genes can be switched on and off. a gene may be turned on when it is supposed to be turned off so cell would have produced a protein that it is not supposed to have at that time. it could lead to uncontrolled mitosis leading to cancer.

46
Q

how many copies of every chromsome do human cells contain

A

two copies of every chromosome.

human cells have 23 pairs of chromosomes.

47
Q

one chromosome in the pair comes from the father, the other chromosome comes from the mother.
as chromosomes come in pairs, how many copies do we have of every gene.

A

we have two copies of every gene

48
Q

definition of alleles

A

alleles are versions of a gene

49
Q

definition of genotype

A

genotype tells us the alleles present

50
Q

definition of homozygous

A

two copies of the same allele.

51
Q

defninition of phenotype

A

phenotype tells us the characteristics caused by the person’s alleles.

52
Q

definition of heterozygous

A

two different alleles

53
Q

definition of dominant allele

A

a dominant allele will always be expressed in the phenotype even if there is only one copy present

54
Q

definition of recessive allele

A

a recessive allele will only be expressed in the phenotype if two copies are present

55
Q

what is cystic fibrosis

A

cystic fibrosis is a disorder of cell membranes.

56
Q

what is the allele for defective membranes

A

recessive

in order to have cystic fibrosis a person needs to have two copies of the defective allele.

57
Q

what is a person with one dominant allele and one recessive allele called in the context of cystic fibrosis

A

a person with one recessive allele only is called a carrier, they do not have cystic fibrosis because in order to have it person needs two copies of the defective alleles.

58
Q

Polydactyly

A

people with polydactyly have extra fingers or toes

59
Q

what type of allele is polydactyly caused by

A

a dominant allele- this means person will have polydactyly even if they have only one copy of the polydactyly alllele.

60
Q

you cannot be a carrier of the polydactyly allele that is true for any dominant allele. if you have a dominant allele you have the

A

characteristic

61
Q

what is one solution to inherited disorders

A

embryo screening- embryos are tested to see if they have the alleles for inherited disorders.

62
Q

explain how embryo screening works

A

-embryos are tested to see if they have the alleles for the inherited disorders, embryos which do not have the defective allele are implanted into the woman, these can develop into healthy offspring.

63
Q

issues around embryonic screening

A
  • embryonic screening is expensive some people think money should be invested elsewhere in the health service.
  • large number of embryos are created but only small number implanted means that some healthy embryos are destroyed some people think that is unethical.
  • in the future we may be able to screen embryos to produce offsprings with desirable features eg taller more intelligent offspring some people think this is unethical
64
Q

what is gene therapy

A

-scientists may be able to correct faulty alleles and use this to treat inherited disorders.

65
Q

a family tree does not show genotypes, what does it show

A

family trees only show phenotype

66
Q

genetic screening detection in genetic screening

A

DNA isolated from embryo
flourecsent probe mixed with embryo dna
probe binds with embryo dna
uv light shows alleles for genetic disorder.

67
Q

how many pairs of chromosomes do human cells contain in the nucleus

A

23 pairs.

Biology paper 2 2022 AQA GCSE Separate science (5 decks)

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