3. reproduction and inheritance

Question 0

What are the steps of fertilisation?

What are gametes?

What is fertilisation?

Answer 0

Gametes are sex cells: the male one being sperm; the female one being an egg.

When they join together it is know as fertilisation. At this point the fused gametes become a zygote.
A the zygot then divides repeatedly, at this stage it becomes an embryo.

Question 1

What are the differences between sexual and asexual reproduction?

Answer 1

In sexual reproduction two parents create non-identical offspring, inheriting characteristics from both parents.

In asexual reproduction a single parent creates genetically identical offspring.

Question 2

describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is adapted for pollination

Answer 2

Insect-pollinated flower:

Brightly coloured, larger petals
Nectar
Scents

Wind-pollinated flower:

Anthers stick out- past other parts of the flower
Stamen will have large surface area.

Question 3

understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation

Answer 3

A pollen will travel down the stigma through a pollen tube, in to the ovule in the carpel.

Here the pollen will fertilise the ovule, forming a zygote (the seed). The carpel (reproductive organ) becomes a fruit.

Question 4

What are the conditions needed for seed germination?

Answer 4

• Water
• warm temperatures (enzymes e.g to break down starch in to maltose)
• oxygen for respiration

Question 5

how do germinating seeds utilise food reserves until the seedling can carry out photosynthesis?

Answer 5

Food reserves are in the cotyleleus, sustain the plant growth until leaves are able to photosynthesis to support the plant.

Question 6

How can plants reproduce asexually by…

natural methods?

artificial methods?

Answer 6

Asexual reproduction: only involves one parent, this can be achieved in two ways by plants:

(Natural method) Runners: e.g strawberries- a second stem extend, when it reaches the ground cells specialise into root cells and a new plant develops.

(Artificial method) Cuttings: a clipping is put in to plant hormones, encouraging the ends to become roots, when placed in soil it will then create another plant.

Question 7

describe the structure and explain the function of the male and female reproductive systems

Answer 7

Male reproductive system:

Testis- produce sperm cells, they are stored in the epididymus
Vas deference- carries sperm to the penis
The prostate- adds fluid to the sperm, creating semen (as does the seminal vesicles)
The urethra- carries sperm to the end of, and out of the penis.

Female reproductive system:

Ovaries- produce eggs
Oviducts- carry the eggs to the uterus, is the site of fertilisation
Uterus- develops the fertilised egg on the placenta
Cervix- entrance to uterus

Question 8

What are the roles of oestrogen and progesterone in the menstrual cycle?

Answer 8

Oestrogen and progesterone are both hormones which effect the menstrual cycle.

Oestrogen: produced in the ovaries; thickens the womb lining; prompts the release of LH.

Progesterone: produced in the corpus lutiem; maintains the lining of the womb

Question 9

describe the role of the placenta in the nutrition of the developing embryo

Answer 9

The embryo can’t breath, digest or excrete.
Blood vessels inside the placenta can absorb the digested food molecules and oxygen that the embryo needs to survive. Waste products will be taken out of the embryo and put back into the mothers blood stream for her to excrete.

Question 10

how is the developing embryo is protected by amniotic fluid?

Answer 10

The fluid (mainly water) cannot be compressed- it absorbs pressure- so any force on the uterus wall will not harm the embryo.

Question 11

What are the roles of oestrogen and testosterone in the development of secondary sexual characteristics?

Answer 11

Secondary sexual characteristics develop during puberty:

Oestrogen- females:

The beginning of the menstrual cycle
Body mass increases and redistributed- to hips and breasts
Body hair- pubic
Voice deepens slowly
Development of sexual organs

Testosterone- males:

Production of sperm
Growth of sexual organs
Body hair- pubic, arms and face
Body mass will increase, including muscle mass
Voice breaks (becomes deeper)
Development of a sexual drive

Question 12

understand that the nucleus of a cell contains chromosomes on which genes are located

Answer 12

In the nucleus of a cell there are chromosomes; these are long sections of tangled DNA, sections of which are different genes.

Question 13

What is a gene?

Answer 13

Different genes code different proteins. Genes are sections of your DNA.

a gene is a section of a molecule of DNA.

Question 14

What is the structure of a DNA molecule?

What are the 2 DNA base pairs?

Answer 14

DNA resembles a ladder (that has been twisted,) on either side of each rung will be a base- they are a base pair:

adenine (A) with thymine (T)
or
cytosine (C) with guanine (G).

Question 15

What are ‘alleles’?

What do they do?

Answer 15

Genes come in a variety of forms: for example the gene that codes for hair can come in many different colours.
These different forms are different alleles, having these differences is where you vary in inherited characteristics (If there was only one allele for hair we would all have exactly the same hair.)

Question 16

Define the terms:

dominant
recessive
homozygous
heterozygous
phenotype
genotype
codominance

Answer 16

Dominant: a dominant allele is the one that will be made

Recessive: a recessive allele will be masked by a dominant one and not visible

Homozygous: if you have two of the same alleles for a gene in one persons DNA

Heterozygous: if you have two different alleles for a gene in in someones DNA

Phenotype: what allele is expressed as a protein

Genotype: what alleles you have in your DNA for a gene

Codominance: when two alleles have equal dominance (they will both be expressed)

By expressed I mean shown as in having brown hair is brown hair allele being expressed; and by masked I mean not expressed.

Question 17

What is the sex of a person is controlled by?

XX= female/male
XY=female/male

Answer 17

One pair of chromosomes (out of 23 pairs) controls the gender of a person.

XX is female; XY is male.

Question 18

What does random fertilisation produce?

Answer 18

Random fertilisation produces genetic variation of offspring

Because gametes contain a random selection of genetic information from each parent, the fertilised egg will be a mix of different genotypes which is why offspring are genetically different to their parents.

Question 19

What is the diploid number?

What is the haploid number?

(Chromosomes)

Answer 19

The diploid number is how many chromosomes each cell is meant to have: 46 in humans (23 pairs).

The haploid number is half of the diploid number: so 23.

Question 20

understand that variation within a species can be genetic, environmental, or a combination of both

Answer 20

Variation in a species is the differences between the members of a species.
Genetic is caused by what genes are inhereted.
Environmental is caused by some action after birth (e.g the sun giving you a tan.)
Some variation is a bit of both…

Question 21

understand that mutation is a rare, random change in genetic material that can be inherited

Answer 21

A mutation is when a gene is copied incorrectly, this gene can be passed down.

It doesn’t happen very often or on purpose.

Question 22

describe the process of evolution by means of natural selection

Answer 22

Evolution is a change in species over a very long time (sometimes into different species.)
Natural selection is survival of the fittest.
What happens is:

A mutation occurs
If the mutation is beneficial, the animal will survive longer and reproduce more
Some of its offspring will inherit the mutation
These offspring will also have better chance of survival, meaning they live longer and reproduce more
Over a long period of time this process is repeated and gradually the mutation becomes a common gene in a species and those with the mutation become the only ones, as those without cannot compete with those expressing the mutated gene

Question 23

understand that many mutations are harmful but some are neutral and a few are beneficial

Answer 23

A lot of mutations are harmful, like genetic diseases; cystic fibrosis.
Some don’t change the chances of survival: like having a different colour hair.
There are a few mutations which are beneficial, for example a insect pollinated plant becoming brighter.

Question 24

understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control

Answer 24

Bacteria experience mutations (the reproduce very frequently so it is not rare.) These mutations can mean that they are no longer affected by a certain antibiotic, this makes it easier for them to survive.

If bacteria evolve to be resistant to drugs we are treating them with then they are difficult to control; sometimes they can be stopped using a different antibiotic, but some are becoming resistant to all the drugs that we know of…

Question 25

What can the incidence of mutations be increased by?

Answer 25

There are things that make you more likely to have a mutated gene, these include:

Exposure to ionising radiation (e.g. gamma rays, X-rays and ultraviolet rays)

chemical mutagens(some chemicals in tobacco)