Sexual Reproduction In Flowering Plants Flashcards Preview

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Flashcards in Sexual Reproduction In Flowering Plants Deck (11):
1

Structure of a flower

Receptacle
- swelling at he base of a flower. It supports the flower

Sepals
- function is to protect the flower when it Is a bud

Petals
- protect the other parts of the flower sometimes attract insects

Stamens
- male part of the flower
- The another produces pollen grains
- The filament supports the anther

Carpels
- female part of the flower
- stigma is the place where pollen lands
- Style connects the stigma to the ovary
- Contains one or more ovules, each ovule produces an egg

2

Formation Of male gametes

Anther composed of 4 pollen sacs

Each pollen sac is lined with an epidermis and a fibrous layer

Each pollen sac has a layer o diploid cells called microspore

These cells divide by meiosis to form a group of 4 pollen cells called a tetrad

The tetrad soon splits apart to form 4 individual pollen grains

The immature pollen grains are called microspores , each has a single haploid nucleus

The nucleus divides by mitosis to form to haploid nuclei
- one of these "Tube Nucleus" does not divide anymore
- The second nucleus "Generative nucleus " divided by mitosis to form two sperm nuclei

The mature pollen grains form a though, patterned outer wall called the exine. The inner flexible wall of the pollen grain is called is called the intine

Pollen grains are formed inside the anther . When they are mature the anther breaks open and the walls of the pollen sacs fold back

Means pollen grains are exposed on the outside dif the anther

3

Formation of female gametes?

- each ovules has two walls called integuments . There's a small opening in integuments called microphyle

The microphyle allows the pollen tube to enter the ovule

Most of the ovules consists of diploid nourishing cells called the nucellus

The megaspore Mother cell is a single diploid cell in the centre of the ovule

Cell divides by meiosis to form the embryo sac

3 of 4 haploid nuclei in embryo sac die

4th nucleus divides by mitosis 3 time stop form 8 haploid nuclei

One of these nuclei becomes the egg nucleus which forms the egg

Two more form the polar nuclei

The egg cell and two polar nuclei are female gametes

The carpel now appears

4

What is pollination?

"Pollination is the transfer of pollen from an anther to a carpel"

"Self- pollination" means that the anther and carpel are on the same plant :cereals, offspring weaker

"Cross-pollination" means that the anther and carpel are on different plants : stronger healthier offspring

Methods of cross- pollination

Wind Animal
Petals: small, green, no scent : large, brightly coloured, scent and nectar

Pollen: Huge Amounts, small, light : Small amounts, large, sticky

Anthers: large, outside petals : small, inside petals

Stigmas: large and feathery, : smaller, rounded, inside petals
Outside petals
Example : grass, conifers : orchids, daisies, dandelions

5

What is fertilisation?

"Fertillization is the union of the male and female gametes"

Pollen grains lands on the stigma and forms pollen tube

Tube nucleus cause pollen tube to grow down through the style and into ovule

Tube nucleus dies

Double fertilization:

One of the male gamete nuclei joins with the egg nucleus to form diploid zygote

The second male gamete with the 2 polar nuclei to form a triploid endosperm

6

How does the seed form ?

After fertilisation the ovule becomes a seed

The triploid endosperm grows rapidly and absorbs nucellus

The zygote grows by mitosis to form the embryo

Embryo consists of a plumule and a radical

As the embryo grows it produces one or two seed leaves or cotlydons. The cotlydons are diploid and absorbs the endosperm to act as a food store in the seed

The walls of the ovule (integuments) become the seed coat(testa)

7

What are the types of seed?

Plants that form a seed with single seed leaf are monocots

Plants with 2 seed leaves are dicots

Presence/ absence of endosperm:

- in monocots the cotlydon absorbs food from endosperm and passes it on to embryo
- At maturity monocots seeds have some endosperm - "Endospermic"

- in ducts the cotlydons absorb food from the endosperm and act as stores


-dicot seeds do not have endosperm at maturity

8

What are fruits?

Seeds produce growth regulators such as auxins which stimulate the production of fruit

A fruit normally forms from the ovary

Fruits protect seeds and help disperse them
- some fruits are dry -- grass and cereal grains
- many fruits are moist and edible -grapes and oranges

Seedless fruit

Formation of fruit without seed is called parthenocarpy

E.g.. bananas oranges

Seedless fruits are produce commercially in 2 ways
- Special breeding programmes
- spraying plants with growth regulators such as axins stimulate them to make seedless fruit

8

What are fruits?

Seeds produce growth regulators such as auxins which stimulate the production of fruit

A fruit normally forms from the ovary

Fruits protect seeds and help disperse them
- some fruits are dry -- grass and cereal grains
- many fruits are moist and edible -grapes and oranges

Seedless fruit

Formation of fruit without seed is called parthenocarpy

E.g.. bananas oranges

Seedless fruits are produce commercially in 2 ways
- Special breeding programmes
- spraying plants with growth regulators such as axins stimulate them to make seedless fruit

9

What is dispersal ?

"Dispersal is the carrying of a seed as far possible from the parent plant"

Benefits:
- To reduce competition
- To increase chances of survival
- To find new areas for growth
- To increase numbers of the species

Methods:

Wind-
- some seeds are very small and blown long distances by wind
- dandelions have feathery parachute for larger seed
- anymore have winged seeds
Water
- Water lilys and coconuts have light air filled fruits that float on water

Animal dispersal
- sticky fruits attach to animal and fall off later e.g. buttercup
- edible fruits like blackberries are eaten, the seeds are not digested and pass out of the animal
Self- dispersal
- some plants explode e.g peas

10

To investigate the effects of water, oxygen and temperature on germination

Place filter paper in the base of four Petri dishes

Add water to filter paper in dishes A,C and D

Place 5 seeds in each Petri dish

Dish C is placed in refrigerator at 4 degrees, other dishes left at room temperature 20 degrees

Dish D place in a jar that contains anaerobic conditions. Anaerobic conditions created using an anaerobic kit that absorbs water

Dish A is control as it has all 3 factors

The dishes are left in place for a few days

Results show seeds need water, oxygen and suitable temperature