Sexual reproduction in plants

Question 1

What are the petals?

Answer 1

Large and colourful in insect pollinated and small+green in wind pollinated.

Question 2

What is the corolla?

Answer 2

A collective term for all petals (a whorl).

Question 3

What is the sepal?

Answer 3

Small green leaf-like structure which protect the flower when in the bud.

Question 4

What is the calyx?

Answer 4

A collective term for all the sepals.

Question 5

What is the receptacle?

Answer 5

The swollen base of a flower, all flower parts are attached to.

Question 6

What does the male stamen consist of?

Answer 6

The anther and filament.

Question 7

What is the anther?

Answer 7

Produces pollen, has 4 pollen sacs, when mature sacs split and release it.

Question 8

What is the filament?

Answer 8

Contains vascular tissue to support anther, transports sucrose and amino acids for formation of pollen grains.

Question 9

Formation of pollen sacs?

Answer 9

An anther contains 4 pollen sacs, each one enclosed by protective fibrous layer. Inside layer is the tapetum (food store of energy for cell division).

Question 10

Formation of male gametes?

Answer 10

Each pollen sac undergoes meiosis I and II to form a tetrad (micro spores).
Develop into pollen grains, undergo mitosis to produce generative and tube nucleus.
Generative divide to form 2 male gametes.
When pollen mature, anther dry and split, called dehiscence and release grains.

Question 11

What is the female reproductive organ made up of?

Answer 11

The carpel, stigma and ovary with ovules inside.

Question 12

What is the carpel?

Answer 12

It consists of the stigma, style and ovary.

Question 13

What is the stigma?

Answer 13

Receives the pollen from the anther.

Question 14

What is the ovary?

Answer 14

Contains the ovules, fertilised ovary becomes a fruit. ( Each ovule contains a female gamete- egg, becomes seed).

Question 15

What is the structure of the ovule?

Answer 15

Each ovary contains one or more. 2 walls of ovule are integuments.
Ovule has small opening called micropyle, where pollen tube enters.
(Nucellus contains cells that provide butrients for growth and on diplod cell 2n).

Question 16

Formation of the female gamete?

Answer 16

The diploid cell divides by meiosis to form 4 haploid cells (megaspores), three degenerate and one survives (n), grows to form the embryo sac. The nucleus undergoes 3 divisions, 8 haploid nuclei formed. One near micropyle is egg cell.
Two nuclei in middle of sac are called polar nuclei.

Question 17

What is pollination?

Answer 17

Pollination is the transfer of pollen from the anther of one plant to the stigma of another.

Question 18

How are insect-pollinated plants adapted?

Answer 18

Nectar and a scent present.
Sticky stigma to collect pollen.
Brightly coloured petals.
Anthers positioned to rub pollen onto insects.
Pollen grains have barbs for hooking onto insect fur.

Question 19

How are wind-pollinated flowers planted?

Answer 19

Pollen grains very small and light, larger numbers of.
Petals are small and green, no need to attract insects.
NO scent or nectary.
Stigma are feathery to catch pollen in wind.
Anthers are exposed to wind so pollen can be blown away.

Question 20

What is cross pollination?

Answer 20

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

Question 21

What is self-pollination?

Answer 21

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

Question 22

Advantages of self pollination?

Answer 22

It can give some genetic variation if cross pollination is not possible.

Question 23

Disadvantages of self pollination?

Answer 23

Self-pollination reduces genetic variation.

There is a greater chance of two undesirable recessive alleles being brought together.

Question 24

First part of fertilisation?

Answer 24

Pollen grain land on stigma (of same species), stigma produces sugary solution, where the grain germinates, producing pollen tube.
Tube secretes enzymes, which digest through tissue of style.
Generative nucleus divides by mitosis to produce 2 male gametes (n).

Question 25

Second part of fertilisation?

Answer 25

Tube reaches ovary, enters ovule through micropyle. Tube nucleus disintegrates and the tip of tube bursts, 2 male gametes released into embryo sac.
One fuses with female gamete to form a zygote (2n)
Other one fuses with both polar nuclei at centre of embryo sac to form a triploid endosperm nucleus. Called double fertilisation, zygote develops into embryo plant, grows into a new plant.

Question 26

Function of the tube nucleus?

Answer 26

Controls the growth of the pollen tube.

Question 27

How does the ovary develop into a fruit?

Answer 27

Water leaves the seed, it dehydrated and therefore all metabolic reaction stop. The seed is said to become dormant. The ovary develops to become a fruit.

Question 28

What are monocotyledons?

Answer 28

(e.g. cereals, maizes) they are plants that have seeds with only one cotyledon (seed leaf).

Question 29

What are dicotyledons?

Answer 29

(e.g. broad beans), these plants have seeds with two cotyledons (seed leaves).

Question 30

What are the parts of the seed?

Answer 30

The embryo is the essential part; radicle develops into root and plumule develops into shoot. 1 or 2 cotyldeons, grow from hypocotyl, may be taken above the ground during germination.
A food store supplies the embryo and growing plant until it can make own by photosynthesis. The store may be either cotyledon or in endosperm. The testa is the tough protective outer covering the seed.

Question 31

About monocotyledon fruit?

Answer 31

E.g. Sweetcorn is a fruit as the ovary wall surrounds seed coat and seed.
Embryo plant has 1 cotyledon.
Endosperm is retained and once the seed germinates, the small cotyledons channels sugars to the growing tip.

Question 32

What are the conditions needed for germination?

Answer 32

Water- nutrients in dry seed need to re hydrated before use, it cracks testa so roots can grow and activates enzymes.
Oxygen- Aerobic respiration for germination, lots of ATP for growth needed.
Temperature- optimum temp for germination is the optimum for enzymes to work, different for all seeds (times of year).

Question 33

How does seed germination happen?

Answer 33

Water enters through micropyle so embryo synthesises amylase. Water softens testa to allow it to split. Embryo releases amylase which hydrolyses starch in cotyledons into maltose. Maltose is absorbed by embryo. Maltose in embryo broken into glucose and used in respiration for energy and growth.

Question 34

Part two of seed germination?

Answer 34

Testa ruptures as radicle grows out. Radicle grows down and plumule (shoot) grows up. Cotyledons below ground use starch for growth. Plumule is bent over and pushes through soil, protects tip from being damaged. When emerges it unfolds and begins to make food through photosynthesis.

Question 35

The effect of gibberellin??

Answer 35

Barley embryo secretes plant growth regulator gibberellic acid, it diffuses through the endosperm to the aleurone layer (cells towards outside of the seed, high in protein). The acid switches on genes in cells, resulting in transcription and translation, produce proteins. Proteases hydrolyse protein, amylase diffuses into endosperm cells to hydrolyse starch. Maltose and AA produced diffuse into embryo plant, where maltose is broken down into glucose.