C22 - Plant Reproduction

Question 1

What’s the endosperm?

Answer 1

The food source surrounding the plant embryo.

Question 2

What is the testa?

Answer 2

The protective layer of the seed / the seed coat.

Question 3

What are cotyledons?

Answer 3

Seed leaves.

Some fully developed seeds lack endosperms because the cotyledons have absorbed them so the cotyledons act as the food source.

Question 4

What are gibberellins?

Answer 4

Plant hormones that act as a signalling molecule to break the dormancy of a seed.

After a seed is exposed to water, gibberellin is released which induces the synthesis of amylase. This breaks down starch in the endosperm by hydrolysis into glucose.

Question 5

What do gibberellins do?

Answer 5

After a seed is exposed to water, gibberellin is released which induces the synthesis of amylase.
This breaks down the starch in the endosperm, by hydrolysis, into glucose.

Question 6

Where are the male and female gametes found within plants?

Answer 6

Male gametes are found within pollen grains.

Female gametes are found in ovules.

Question 7

How do plants reproduce?

Answer 7

Pollen from the anthers of one plant must be transferred to the stigma of the other by wind, animals or insects.

Question 8

What are the components of a plant?

Answer 8

Stigma - part of plant that receives pollen

Style - extension above the ovary holding the stigma

Anther - part of stamen containing pollen

Filament - extension holding the anther

Sepal - part of base of flower enclosing the petals

Petal

Ovary

Question 9

What 2 environmental factors can plants detect?

Answer 9

Temperature

Day length : night length ratio (known as photoperiods)

Question 10

What’s photoperiodism?

Answer 10

The response by an organism to synchronise its body with changes in day length.

This is important as change in day lengths indicate seasons and so some plants regulate their flowering accordingly.

Question 11

What happens during photoperiodism?

Answer 11

Change in day length causes the photoperiod mechanism to occur in leaves by the florigen hormone.
This causes the plant to bud and flower.

Question 12

What are long day plants?

Answer 12

Plants which flower during late spring when day length is above critical value (>9-16h).

Question 13

What are short day plants?

Answer 13

Plants which flower when nights are longer and day length is below a critical value (<9-16h).

Question 14

What are day neutral plants?

Answer 14

Plants that do not respond to day length.

Question 15

What is nightbreak phenomenon?

Answer 15

For plants with a critical night length, a short flash of light in the middle of the night would make the plant behave as though it had been exposed to a long day.

Question 16

What’s a phytochrome molecule?

Answer 16

A protein bonded to a non-protein light absorbing pigment molecule.

Question 17

What 2 types of non-protein light absorbing pigment molecule components exist within plants?

Answer 17

Pr - phytochrome red (absorbs red light)

Pfr-phytochrome far red (absorbs far red light)

Question 18

How are Pr and Pfr used within plants?

Answer 18

Formation of phytochrome far red results in developmental processes occurring.

Red light is absorbed by phytochrome red which converts it to Pfr for developmental processes.

This however is reversible and reverts back to Pr in the dark.
Back and forth conversions allow the plant to measure day length

Question 19

How do plants respond to temperature?

Answer 19

A set number of heat units are are required by the plant between developmental stages.

Temperate species must be exposed to low temperatures for an extended period before they can flower, known as vernalisation.

Question 20

What’s vernalisation?

Answer 20

The cooling of a seed during germination to accelerate flowering when planted.

Some flower after vernalisation without further environmental signals.

Question 21

What is hermaphroditism?

Answer 21

Having male and female gametes.

Most species of plant are hermaphroditic.

Question 22

What’s cross pollination?

Answer 22

When pollen from the anther of one flower is transferred to the stigma of another flower.

Question 23

What’s self pollination?

Answer 23

When pollen from the anther of one flower is transferred to the stigma of another flower on the same plant.

Question 24

How does fertilisation occur within plants?

Answer 24

The nucleus of the male gamete in the pollen fuses with the nucleus of the female gamete in the ovules.

Each pollen grain grows a pollen tube down into the ovule. One pollen tube reaches the ovule where a nucleus of a male cell joins with the nucleus in the female cell.

Question 25

What are plant wind-pollination adaptions?

Answer 25

They don’t need to be bright, scented or have nectar to attract insects.

Instead, they have large quantities of light pollen grains which can be carried through air in plentiful amounts in case some fail to reach other plants.

Question 26

What are the various parts of a plant seed’s structure?

Answer 26

(External)
Seed coat (testa)
Scar where seed was attached to ovary

(Internal)
Embryo shoot (plumule)
Embryo root (radicle)
Cotyledon 
Seed coat

Question 27

What’s the purpose of a pollen tube in plants?

Answer 27

To allow the passage of male gametes into the ovary, where they’ll fertilise the ovule.

The pollen tube down the style delivers 2 sperm cells from the stigma to the ovules at the same time.

One fertilises an egg to form an embryo which will develop into a future plant.
The nucleus of the other sperm cell will fuse with the 2 polar nuclei at the centre of the embryo sac to form the endosperm which acts as the embryo’s food supply.
This is known as double fertilisation.

The ovules develop into seeds, which contain the embryo and endosperm.

Question 28

How does double fertilisation occur in plants?

Answer 28

The pollen tube down the style delivers 2 sperm cells from the stigma to the ovules at the same time.

One fertilises an egg to form an embryo which will develop into a future plant.
The nucleus of the other sperm cell will fuse with the 2 polar nuclei at the centre of the embryo sac to form the endosperm which acts as the embryo’s food supply.

This is known as double fertilisation.

The ovules develop into seeds, which contain the embryo and endosperm.

Question 29

What does the endosperm contain?

Answer 29

It’s a tissue surrounding the plant embryo within a seed, consisting primarily of starch although it often contains oils and proteins.

It acts as a food source for the embryo.

Question 30

What makes cereals good staple foods?

Answer 30

The nutrition of many staples e.g. rice, maize, wheat etc is from the endosperm of plants which can be used for humans.

The endosperm is rich in starch and is therefore a good source of carbohydrate.