REPRODUCTION IN PLANTS Summarized Biology Notes

BIOLOGISEDTEAM™

15 Jun, 2022

REPRODUCTION IN PLANTS:

FOCUS OF THIS TOPIC

●Flower structure and function

●Pollination: Self pollination & Cross pollination.

●Fertilization: Double fertilization.

●Seed and fruit: Formation and dispersal

SEXUAL REPRODUCTION IN PLANTS

Learning outcomes:

• Describe the structure and functions of the flower of a named dicotyledonous plant

• Define pollination as the transfer of pollen from an anther to a receptive stigma

• Distinguish between self-pollination and cross- pollination name the agents of pollination

• Compare the different structural adaptations of insect-pollinated and wind pollinated flowers

•Describe the growth of the pollen tube and the process of double fertilization (no details of ovule and embryonic sac).

•Describe the formation of seeds and fruit.

•Describe the structure of a non-endospermic seed.

•Define dispersal of seeds and fruits.

•Describe adaptations of seeds and fruit dispersed by wind, water, animals and self.

A FLOWER

• Some plants produce asexually and some

produce sexually.

•The reproductive part of those plant that reproduce sexually is called a FLOWER.

• The flower: is an sexual organ of sexual reproduction in flowering plants (angiosperms).

• It is where the sex cells of the plants are produced and join to form seeds.

Flowers can be either Unisexual flowers or Bisexual flower

a) Bisexual flower: has the stamen and carpels in the same flower

b) Unisexual Flowers: has Stamen (male organs) and Carpel (female organs) on separate flower

Looking at the flower structure. It consist of:

•Receptacle

•Stalk (stem)

•Calyx(Sepaís)

•Petals

•Carpel

•Ovary

•Ovule

•Female gametes

•Stigma

•Style

•Stamen

•Anther

•Filament

•Male gamete

•Nectar gland/nectary

•Nectar

THE FLOWER

●Receptacle: the top of the flower stalk which is expanded and which bears the parts of the flower.

●Stalk (peduncle):

✓ holds the whole flower and connect it to the stem.

✓ Carries inorganic & organic nutrients to the flower.

●Calyx (Sepals):

✓ are bight or dull structure, that produce scented and coloured to attract insect.

✓ Protect the flower while it is in developing in the bud stage.

●Petals:

✓ with bright colour and smell (scented) to attract insects for pollination.

●Nectar gland/ nectary:

✓ A swelling found on the receptacle or other parts of some flowers which produces nectar.

●Nectar:

✓ is a sweet sugary solution produced by nectaries. Insects and bird feeds on nectar and pollinate the flower.

THE STAMEN

●Stamen: is the male reproductive structure or organs of the flower consist of an anther and filament.

✓Anther. produce pollen grains (the male

gamete /sex cells).

✓Filament: the thin stem that holds the anther in position expose it to agents of pollination.

✓Male gamete: the haploid sex cell which fuse with the female gamete during fertilisation to form the diploid zygote.

THE CARPEL

●Carpel (pistil): -the female reproductive structure or organs of the flower consist of a stigma, style, ovary and ovule.

✓ Stigma: -receptive tip of style that receive pollen from the anther during pollination. It also. produce nutritive materials for pollen to germinate

✓ Style: -the swollen part from the stigma to the bottom of the carpel (ovary) which is the path through which the pollen tube grows on its way to the ovary for fertilisation.

- extent out the stigma to be exposed agent of pollination.

✓ Ovary: -the base of the carpel that contain the

female sex cells (the ovules) and develop intot he fruit after fertilization.

✓ Ovules: -located within the ovary that contain the female gametes and develop into a seed after fertilisation.

✓ Female gamete: the haploid sex cell (ovum)

which fuse with the male gamete during fertilisation to form the diploid zygote.

POLLINATION

•Is the transfer of pollen from the anther to the

receptive stigma of the same species.

•The male gamete travel as a pollen grain from

the anther to the stigma and join within the ovule to form a seed.

•This require agents of pollination, such as:

✓ Animals such as birds

✓ insects

✓ Wind

✓ Water

✓ Humans

INSECT POLLINATION

•Insect pollination: is the transfer of pollen to the

receptive stigma by insects. The flowers are called insect-pollinated flower.

Adaptations of insect pollinated flower

★ Have large, conspicuous petals, often with guidelines.

★ Anther inside the flower, where insect has to brush past them to get to nectar.

★ Have an attractive smell (scent).

★ Produce nectar.

★ Sticky pollen to stick on animal body.

★ Quite large quantities of pollen made as some will be eaten or carried to the wrong sort of flower.

★ Smaller Stigma are sticky, not feathery.

WIND POLLITION

•Is the transfer of pollen from anther to the receptacle stigma by wind. The flower are called wind-pollinated flower.

Adaptations of wind pollinated flower.

★Smell and dull coloured.

★Do not produce nectar.

★ Do not produce smell (no scent).

★ Have large feathery anther hanging outside the flower shaking in the wind.

★ Produce very large amount of pollen as most of it is lost in the wind.

★ Smooth, light pollen which can be blown in the wind.

POLLINATION CAN TAKE PLACE IN 2 WAYS:

1. Self-Pollination: is the transfer of the pollen the anther to the stigma within the same flower or between flower of the same plant.

2. Cross-Pollination: Is the transfer of pollen from the anther of one flower to the stigma of flower of another plant same species.

Implications of self pollination

Disadvantages of Self-Pollination:

✓ Reduce the amount of genetic variety in a population.

✓ Reduce resistance to parasites and diseases-

causing organisms.

Advantages of Self-pollination:

✓ Allow pollination at environment where insects and other pollinators are scares.

✓ Plant with good characteristics pass them to offsprings.

Implications of cross pollination

Advantages of Cross-Pollination:

✓Ensure greater genetic variety in a population.

✓ Greater resistance to different environment conditions.

✓ Increase the chance of survival.

✓ Greater ability for plants to adapt.

Disadvantages of Cross-Pollination:

✓ A lot of pollen is wasted as insects eat up some pollen and blown away by wind.

THE GROWTH OF THE POLLEN TUBE AND FERTILIZATION

THE GROWTH OF THE POLLEN TUBE:

• After pollination, the male gamete is inside the

pollen grain on the stigma.

• The male gamete has to reach the female gamete inside the ovule which is inside the ovary.

• On the same species flower, the pollen grain absorb sugar fluid secreted by the structure stigma an germinates.

• Germination causes pollen tube to grow down into the stigma through the style to the ovary.

• The pollen tube digest the style using enzymes and enters ovary.

• It passes through the micropyle into the ovulen and then into the embryo sac.

FERTILIZATIO IN PLANTS (Double

fertilization).

• The pollen tube has two types of nuclei.

• One nucleus divides into 2 haploid male gametes.

• After the pollen tube penetrate to the ovule, it then release 2 haploid male gametes.

• This is followed by 2 important processes:

1. One haploid male gamete nucleus passes into the embryo sac and fuses with a female gamete (egg) nucleus forming a diploid zygote. The diploid zygote divides by mitosis to form the embryo plant.

2. One second gamete nucleus passes further into the embryo and fuses with the 2 polar nuclei

in the ovule to form a triploid endosperm nucleus.

* The endosperm nucleus divide by mitosis to form endosperm tissue.

* The cells in endosperm are filled with stored food material, providing reserves for the developing embryo.

This process of 2 fusion of a female gamete and 2 polar nuclei is called Double Fertilization.

Summary of Fertilization

1. A pollen tube grows from pollen grain, down the style, through the micropyle and into the ovule.

2. Two sperm nuclei are discharged into the embryo sac resulting in double fertilization.

3. The fertilized egg (zygote) will develop into the embryo.

4. The ferilized central cell will develop into endosperm.

5. The ovule develops into a seed.

6. The ovary develops into a fruit containing one or more seeds.

AFTER FERTILIZATION

formation of the fruit and seed

a) Formation of the fruit:

• Most of parts of the flower dry up and fall off.

• This include: sepals, petals and stamen.

• The ovary develop into a fruit: to protect the seed inside it until they are ripe.

b) Formation of the seed:

• The seed develop from the ovule. The ovules start to grow with the zygote in each ovule.

•The zygote divides by mitosis forming an embryo plant.

• The embryo plant consists of the radicle (developing root) and plumule (developing stem/

shoot), between a single or two cotyledons (seed lobes).

• The triploid endosperm nucleus divides repeatedly by mitosis to form the endosperm which is the food store.

• In the case of dicotyledonous plant endosperm (food store) is held in the cotyledons.

• The two layers that cover the ovule(integument)

develop into a tough, hard outer coat called a testa.

• The content of the testa (ovule) loses water, and the whole structure become a seed.

THE INTERNAL STRUCTURE OF A NON ENDOSPERMIC SEED

LOOK AT THE EXTERNAL APPEARANCE AND INTERNAL OF A SEED

SEEDS AND FRUIT

• FRUITS: apart from protecting the seeds inside until they are ripe. They also helps to disperse the seeds.

• DISPERSAL: is the spreading out of seeds and fruits as far as possible from the parent plant. Seeds and fruit can be dispersed through:

a) Wind dispersal

b) Animal dispersal

c) Water dispersal

d) Self dispersal

IMPORTANCES OF SEED AND FRUIT DISPERSAL

1. Reduces competition for resources among parents and offspring due to overcrowding (i.e competition for water, light, nutrient, space etc)

2. Allow plant to colonise new areas for them to grow far from parents.

3. Broad distribution leading to increased biodiversity.

4. Decrease the risky of spread of pests and diseases

5. Reduce the risky of extinction of communities

of species in cases of natural disasters (i.e. fire, and disease outbreak).

WIND DISPERSAL

ADAPTAION OF WIND DISPERSAL SEEDS

AND FRUITS

• Very light in weight.

• Small in size with flattened wing-like structures to allow it to be carried (blown) by wind.

• Some have feathery hair increasing surface are "flight" over long distances i.e. dandelion seeds.

ANIMAL DISPERSAL: JUICY FRIT (BLACKBERRY, STRAWBERRY): CATCHING ON FUR (GOOSEGRASS, BURDOCK).

ADAPTATION OF ANIMAL DISPESAL

SEEDS AND FRUITS

• Coloured, sweet and juicy to attract birds (animals) to eat them and be dropped in faeces

I far places. i.e. tomatoes, guava, and wild berries.

• Some have hooks to catch on the fur of mammals and be dropped far away.

• Succulent fruits i.e. marula and strawberry have seeds which can through the digestive system of animals unharmed and are carried long distance before deposited along with fertilizer on the ground.

WATER DISPERSAL: COCONUTS, Watter lily etc

• Generally, light in weight and waterproof.

• Have large surface area for floating on water.

SELF DISPERSAL: LIPIN SEEDPODS, GERAINIUM FRUIT

ADAPTATION OF SELF DISPERSAL SEEDS

AND FRUITS

• Some plants have mechanisms which throw seeds some distance from the parent plant.

• It depends on tension caused by drying out of the fruit wall.

• The sweat pea suddenly split open and the two

halves curl outwards, scattering the seeds.

• Some fruits scatter their seeds by literally exploding. The pod dries; bursts open and forcibly shoot the seeds for several feet in all directions.

SEED GERMINATION

THE GENERAL CYCLE OF FLOWERING PLANTS

• Germination: is the onset of growth of the embryo plant in the seed after a period of dormancy.

✓ Once the seed land on the suitable environment: adequate water, oxygen and optimum temperature; enzymes and stored food substances are activated and the embryo plant start to grow.

STAGES OF SEED GERMINATION

• The seed take up water through the micropyle.

• The cotyledon swell, causing the testa (seed coat) to burst.

• This activate the enzymes to digest stored insoluble nutrients such as protein, carbohydrate and fats into soluble ones such as glucose, amino acids and fatty acids.

• The soluble nutrients diffuse to the embryo plant to provide energy and stimulate growth.

•The radicle develop into a root to absorb water from the soil.

• The plumule develop into the shoot to absorb sunlight and carry out photosynthesis.

ARE YOU ABLE TO????

DEFINE:

•A flower

•Pollination

•Fertilization

•Double fertilization

•Gametes

•Dispersal

ARE YOU ABLE TO: