B13

Question 1

What does sexual reproduction involve?

Answer 1

Sexual reproduction involves a male gamete (sex cell) and a female gamete (sex cell) from 2 parent cells.

Question 2

How are gametes produced?

Answer 2

Gametes are produced by meiosis

Question 3

What is fertalisation?

Answer 3

It is when gametes fuze together

Question 4

Why is there variation in offspring?

Answer 4

The genetic information from both gametes is mixed, this leads to variation in the offspring

Question 5

How is the sperm cell specialised to carry out it’s function?

Answer 5

The nucleus contains the genetic information to pass on.

A long tail helps the sperm to move to reach the egg.

There are lots of mitochondria to transfer the energy needed for the tail to work.

The acrosome stores enzymes that allow the sperm to break through the egg membranes.

Question 6

How does sexual reproduction happen in plants?

Answer 6

The gametes in plants are pollen and egg cells.

The egg cell is found inside the ovary of the flower.

The pollen is produced by the anther.

When pollination occurs, the pollen and the egg cell meet and fuse in fertilisation.

The genetic information from both gametes is mixed, this leads to variation in the offspring.
The fertilised cell forms seeds.

Question 7

What is asexual reproduction?

Answer 7

It involves only one parent.

There is no fusion of gametes, therefore there is no mixing of genetic information.

Only mitosis is involved.

It produces genetically identical offspring (clones).

Question 8

What are the advantages of sexual reproduction over asexual reproduction?

Answer 8

Offspring from sexual reproduction have a mixture of two sets of chromosomes. The organism inherits genes (and therefore features) from both parents, which produces variation in the offspring

Variation increases the chance of a species surviving a change in the environment. While a change in the environment could kill some individuals, it’s likely that variation will have led to some of the offspring being able to survive in the new environment. They have a survival advantage.

Because individuals with characteristics that make them better adapted to the environment have a better chance of survival, they are more likely to breed successfully and pass the genes for the characteristics on. This is known as natural selection

We can use selective breeding to speed up natural selection. This allows us to produce animals with desirable characteristics. Selective breeding is where individuals with a desirable characteristic are bred to produce offspring that have the desirable characteristic too. This means that we can increase food production, e.g. by breeding animals that produce a lot of meat.

Question 9

What are the advantages of asexual reproduction over sexual reproduction?

Answer 9

1) There only needs to be one parent

2) This means that asexual reproduction uses less energy than sexual reproduction, because organisms don’t have to find a mate.

3) This also means that asexual reproduction is faster than sexual reproduction.

4) Many identical offspring can be produced in favourable conditions.

Question 10

Whats the difference between mitosis and meiosis?

Answer 10

Mitosis:
•Produces two daughter cells.
• Daughter cells are genetically identical.
• The cell divides once.
• The chromosome number of the daughter cells is the same as the parent cells.
• Used for growth and repair, and asexual reproduction.

Meiosis:
• Produces four daughter cells.
- Daughter cells are not genetically identical.
• The cell divides twice.
• The chromosome number is reduced by half.
• Produces gametes.

Question 11

What does meisosis do?

Answer 11

Meiosis produces cells with half the normal number of chromosomes

Question 12

What is fertalisation and variation?

Answer 12

-when the sperm and egg come together, fertilisation takes place

• Each egg and sperm have 23 chromosomes, half the number of chromosomes.

• When they join, they form a single new body cell which contains the full 46 chromosomes (23 pairs)

• This is the correct number of chromosomes for a human body cell.

• The combination is unique and creates variation in the species.

Question 13

What organisms reproduce by both methods : asexual and sexual reproduction

Answer 13

• Malarial parasites reproduce asexually in the human host, but sexually in the mosquito.

• Many fungi reproduce asexually by spores but also reproduce sexually to give variation.

• Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.

Question 14

What is DNA?

Answer 14

DNA is a polymer that is made up of four different nucleotides. Two strands twist together to form a double helix.

Question 15

What is a nucleotide?

Answer 15

Each nucleotide is made of a sugar and phosphate group with one of four different bases attached.

Question 16

What are the bases and what are they linked to?

Answer 16

The four bases are A, C, G and T. The C base is always linked to a G base on the complementary strand. An A base is always linked to a T base on the complementary strand.

Question 17

What is a gene?

Answer 17

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids and that makes a specific protein.

Question 18

When are dominant alleles expressed?

Answer 18

They are always expressed even if only one of the alleles is dominant

Question 19

When is the reccesive alleles expressed?

Answer 19

When both of the alleles are recessive

Question 20

Homozygote meaning

Answer 20

An individual with 2 identical alleles for a characteristic for e.g. BB, bb

Question 21

Heterozygote meaning

Answer 21

An individual with different alleles for a characteristics for e.g. Bb

Question 22

Genotype meaning

Answer 22

The genotype is the collection of alleles that determine an organism’s characteristics

Question 23

Phenotype meaning

Answer 23

This describes the physical appearance of a particular characteristic for e.g. black fur or brown fur

Question 24

What does the sugar and phosphate form in a nucleotide ?

Answer 24

It forms a sugar phosphate back bone

Question 25

Explain the whole process of protein synthesis

Answer 25

• Proteins are made in the cell cytoplasm in tiny structures called ribosomes

1) To make proteins, ribosomes use the code in DNA. DNA is found inside the nucleus and it can’t move out of it because it’s really big. So the cell needs to get a code from the DNA to the ribosome

2) This is done by a molecule called mRNA - which is made by copying the code from DNA. The mRNA acts as a messenger between the ribosome and DNA - it carries the code between the two

3) The correct amino acods are brought to the ribosomes in the correct order by carrier molecules

Question 26

What are mutations ? And what do they do ?

Answer 26

Mutations are changes to genetic code

Mutations change the sequence of the DNA bases in a gene, which produces a different form of a gene (generic variant). As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for.

But most mutations have very little or no affect on the protein
But sometimes the mutations do affect the protein and this could affect its ability to perform a function

Question 27

What happens if there is a mutation in the non-coding DNA ?

Answer 27

It can alter how genes are expressed

Question 28

What are the 3 different types of mutations ?

Answer 28

Insertions - it is where a new base is inserted into the DNA base sequence where it shouldn’t be and this changes the way that the 3 bases are ‘read’ which can change the amino acids that they code for

Deletions - it is when a random base is deleted from the DNA base sequence, this changes the way that the 3 bases are ‘read’ and has knock on effects futher down the sequence

Substitutions - it is when a random base in the DNA base sequence is changed to a different base

Question 29

Each amino acid is coded for by a sequence of …. bases in the gene

Answer 29

3

Question 30

What are non-coding parts of genes?

Answer 30

They are parts of DNA that dont code for proteins

Question 31

Explain the meiosis process

Answer 31

When a cell divides to form gametes: (meiosis)
• copies of the genetic information are made
• the cell divides twice to form four gametes, each with a single set of chromosomes
• all gametes are genetically different from each other.

Question 32

What is cystic fibrosis and what is it caused by ?

Answer 32

Cyctic fibrosis is caused by a recessive allele

Cystic fybrosis is a genetic disorder of the cell membranes where the body produces a lot of thick sticky mucus in the air passage and in the pancreas

Because it’s recessive, people with only one copy of the allele won’t have the disorder - they’re known as carriers

Question 33

What is Polydactyly ? And what is it caused by ?

Answer 33

Polydactyly is a genetic disorder where a baby’s born with extra fingers or toes. It doesn’t usually cause any problems so it’s not life threatening

It’s cause by a dominant allele so it can be inherited if only one parent has it

Question 34

What is embryo screening ?

Answer 34

1) During in vitro fertilisation (IVF), embryos are fertilised in a laboratory, and then implanted into the mother’s womb.
2) Before being implanted, it’s possible to remove a cell from each embryo and analyse its genes.
3) Many genetic disorders can be detected in this way, such as cystic fibrosis.
4) It’s also possible to get DNA from an embryo in the womb and test that for disorders.
5) There are lots of ethical, social and economic concerns surrounding embryo screening.

Question 35

What are the arguments for and against embryo screening ?

Answer 35

For:
1) It will help to stop people suffering.
2) Treating disorders costs the Government (and the taxpayers) a lot of money.
3) There are laws to stop it going too far.
At the moment parents cannot even select the sex of their baby (unless it’s for health reasons.

Against:
1) It implies that people with genetic problems are ‘undesirable’ this could increase prejudice.
2) There may come a point where everyone wants to screen their embryos so they can pick the most ‘desirable one, e.g. they want a blue-eyed, blond-haired, intelligent boy.
3) Screening is expensive.