3.1-3.7 Reproduction part 1

Question 1

What is Sexual reproduction?

Answer 1

The process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg) and for production of offspring that are genetically different to each other

Question 2

What is a Gamete?

Answer 2

A gamete is a sex cell (sperm ovum)

Question 3

Why do gametes differ from normal cells

Answer 3

Gametes contain half the number of Chromosomes found in other body cells (haploid cells)
one copy of each chromosomes gametes contain 23 chromosomes

Question 4

What is a zygote?

Answer 4

When the male and female gamete fuse they become a zygote (fertilised egg)
Contain the full 46 chromosomes half from father half from mother zygotes are diploid

Question 5

What are the advantages of Sexual reproduction?

Answer 5

Increased genetic variation
Species can adapt to environment due to variation giving survival advantage
Disease less likely to affect population

Question 6

What are the disadvantages of sexual reproduction

Answer 6

Takes time and energy to find mate
difficult for isolated members of species to reproduce

Question 7

What is Asexual reproduction?

Answer 7

The process resulting in genetically identical offspring being produced from one parent.

Question 8

Why does Asexual reproduction not need gamates

Answer 8

Only one parent is required so there is no fusion of gametes and no mixing of genetic information
As a result, the offspring are genetically identical to the parent and to each other (they are clones)

Question 9

Give an example of a Asexual reproduction

Answer 9

Bacteria produce exact genetic copies of themselves called binary fission
Many plants reproduce via asexual reproduction

Question 10

What are the Advantages of Asexual reproduction?

Answer 10

Population can be increased Rapidly when conditions are right
Can exploit suitable environments quickly
More time and energy efficient
reproduction is complete much quicker than sexual reproduction

Question 11

What are the key differences between sexual and asexual reproduction?

Answer 11

The number of parent organisms
How offspring are produced (the type of cell division required)
The level of genetic similarity between offspring
The possible sources of genetic variation in offspring
The number of offspring produced
The time taken to produce offspring

Question 12

What is Fertilisation

Answer 12

the fusion of gamete nuclei, and as each gamete comes from a different parent, there is variation in the offspring

Question 13

What are the reproductive organs of plants?

Answer 13

Flowers

Question 14

What is the male gamete in a plant

Answer 14

Plants produce pollen, which contains a nucleus inside that is the male gamete

Question 15

How is the gamete of a plant different to that of a humans?

Answer 15

Unlike the male gamete in humans (sperm), pollen is not capable of locomotion (moving from one place to another)

Question 16

What is pollination?

Answer 16

plants mechanism to transfer pollen from the anther to the stigma.

Question 17

What are the two main types of mechanisms

Answer 17

Pollination where the pollen is transferred by insects
Pollination where the pollen is transferred by the wind

Question 18

Name the parts of the plants and their functions for asexual reproduction?

Answer 18

Sepal- protects unopened flower
Petals- bright coloured to attract insects
Anther- produces and releases the male sex cell (pollen grain)
Stigma- top of the female part of the flower collects pollen grains
Ovary- produces the female sex cell
Ovule- contains the female sex cell.

Question 19

Explain the proccess of asexual reproduction for an insect pollinated flower?

Answer 19

As an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect’s body
When the insect visits another flower, it may brush against the stigma of this second flower and in the process, may deposit some of the pollen from the first flower, resulting in pollination

Question 20

Explain the proccess of asexual reproduction for an insect wind-pollinated flower?

Answer 20

When ripe, the anthers open and shed their pollen into the open air
The pollen is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination

Question 21

What is cross pollination

Answer 21

Cross-pollination occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
This is the way most plants carry out pollination as it increases the genetic variation in the offspring

Question 22

What is self pollination
and why is it bad?

Answer 22

Occasionally, the pollen from a flower can land on its own stigma or on the stigma of another flower on the same plant - this is known as self-pollination

Self-pollination reduces the genetic variation in the offspring as all the gametes come from the same parent (and are therefore genetically identical)
Lack of variation in the offspring is a disadvantage if environmental conditions change, as it is less likely that any offspring will have adaptations that suit the new conditions well

Question 23

What is a pollen tube

Answer 23

Unlike the male gametes in animals (sperm), the pollen grain has no ‘tail’ to swim to the ovary of the flower
Instead, in order to reach the ovum nucleus, the pollen grain grows a pollen tube
This only happens if the pollen grain has landed on the right kind of stigma

The nucleus inside the pollen grain moves down the tube as the tube grows down the style towards the ovary (which contains the ovule that, in turn, contains the ovum)
Once the nucleus of the pollen grain and the nucleus of the ovum have fused (joined together), that particular ovule has been fertilised and a zygote has been formed
The zygote will then start to divide (it is the structure that eventually develops into an embryo plant)

Question 24

What happenes after fertilisation for a plant?

Answer 24

After fertilisation, the ovule (that contains the zygote) develops into the seed
The wall of the ovule develops into the seed coat, known as the testa
The parts of the flower surrounding the ovule (mainly the ovary walls) develop into the fruit, which contains the seeds
The fruit provides a mechanism for seed dispersal (getting the seeds away from the parent plant)
Some fruits are eaten by animals, which then disperse the seeds in their droppings (the tough outer coat of seeds stops them from being digested)
Some other fruits have sticky hooks that get caught in the fur of passing animals

Question 25

Why do different fruits have a different number of seeds?

Answer 25

As different plants have different numbers of ovules, this explains why different fruits have different numbers of seeds (which develop from the ovules)

Question 26

What is Germination?

Answer 26

Start of growth in the seed, the seed contains the zygote which divides into cells that develop an embryo plant

Question 27

Explain the process of Germination

Answer 27

When the seed germinates, this embryo begins to grow into the young seedling
Structures known as cotyledons surround the embryo
The cotyledons contain food reserves that supply the young seedling with food (energy)
The cotyledons fulfil this role until the young plant grows its own leaves and becomes capable of making its own food via photosynthesis
After taking in water, the seed coat (testa) splits
This leads to the production of the plumule

Question 28

How can Asexual reproduction occour in plants?

Answer 28

Some plants grow side branches, known as runners, that have small plantlets at their ends
Runners are horizontal stems that grow sideways out of the parent plant
Once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant

Question 29

How does artificial Asexual reproduction occour in plants?

Answer 29

Simple method to clone plants is to take cuttings artificial method
Gardeners take cuttings from good parent plants (healthy)
A section of the parent plant with a new bud is cut off it will then be placed into water to grow new roots or sometimes just into soil.
Sometimes the stem of the cutting may be dipped into rooting powder to increase plant growth the plant is then planted and will grow to an adult genetically identical to the original plant. Very cheap and quick

Question 30

What are the features of an insect pollinated plant?

Answer 30

Question 31

What are the features of Wind pollinated plants?

Answer 31

Question 32

Explain the practical conditions for germination?

Answer 32

Set up 4 test tubes, with each containing 10 cress seeds on cotton wool
Label the test tubes A, B, C and D
For test tube A, leave the cotton wool dry
For test tube B, add enough water to the cotton wool so that it becomes moist
For test tube C, add enough water to cover the cotton wool and seeds, then carefully add a layer of oil on top of the water
For test tube D, add enough water to the cotton wool so that it becomes moist
Leave tubes A, B and C at room temperature or incubated at a specific temperature (e.g. 20°C)
Place tube D in a fridge (approximately 4°C)
Leave all tubes for a set period of time (e.g. 3 - 5 days)
Ensure the cotton wool in tubes B and D remains moist throughout this time by adding more drops of water if required
Compare the results and see which tube has the greatest number of germinated seeds

Question 33

What are the results and analysis for this experiment?

Answer 33

The test tubes are set up so that each of the factors required for germination (water, oxygen and warmth) can be tested, by selectively removing each in turn
In test tube A, water is removed
Test tube B is the control tube, where all factors are present
In test tube C, oxygen is removed (oxygen cannot pass through the oil and water layers on top of the seeds)
In test tube D, warmth is removed
As germination cannot occur if the conditions are not right (i.e. if even one of the three factors required is absent), it would be expected that only the seeds in the control tube will germinate