4.2 SEXUAL REPRODUCTION IN PLANTS

Nectar function

Attract insects and pollinaters

Effective pollen transfer

Anther and stigma touch same part of bee

Prevent self pollination

Protandry Stigma mature before anther or protogony

Anther is below the stigma

Function of generative male nucleus

Fertilisation contain gametes formation of endosperm

Function of tube nucleus

Control growth of pollen tube through style

Produce enzymes to digest style

Conditions for germination

Water

• Cotyledons swell and testa soften

• Transport dissolve substances fluid medium for enzymes

Oxygen

• Aerobic respiration ATP for metabolism

Suitable temperature

• Speeds up rate of diffusion

• Increase enzyme activity

Germination gibberellin, maize (dicot)

Non Endospermic

Imbibition - water

• Water enter micropyle Cotyledons swell

• Testa split Oxygen enter (aerobic)

• Food reserver from cotyledons

Enzyme

• Amylase digesting starch from cotyledons → maltose →Maltase→ glucose

• Proteins and fats

• ATP cell division, active transport, protein synthesis radicle plumule meristem sink

Emerging

• Radicle emerge micropyle to root anchor absorb water Elongates cotyledons pushed - shoot

Photosynthesis begin

Germination of maize gibberellin (monocot)

Endospermic

Imbibition

• Water enter micropyle seed swell

Starch protein fats in endosperm

Embryo produce Gibberellic acod (GA) by embryo

Hormone

• GA diffuse → endosperm→ aleurone layer (protein rich)

• GA switch genes aleurone layer - protein synthesis form enzymes

• Protease hydrolyse aleurone layer → amino acids

• Amino acids used to synthesis amylase

• Amylase diffuse out aleurone → hydrolyse starch stored in endosperm

Glucose → endosperm → plumule and radicle

aerobic respiration ATP

Growth of seedling

Radicle emerge (root)

Plumule emerge up

Monocot - plumule has coleoptile

Radicle - coleorhiza protects

ATP in embryo

Cell division (mitosis)

Active transport

Growth

Double fertilisation

• One nucleus fuse with ovum → Zygote

• One nucleus fuse with 2 polar nuclei → endosperm nucleous

Disadvantage of self pollination

Less genetic variation risk of genetic faults

Pollen grains enable adaption terrestial

Pollen tube deliver male gametes to ovule n

No need for water /mobile gametes

Transferred via wind or insects

Broad bean structure and from where

Fruit- fertilised ovary

Embryo - zygote

Testa - integuments

Seed - ovule

Insect pollinated flower structure

Stamen

• Anther + Filament

Carpel

• Stigma + Style

• Ovary + Ovule + Embryo sac

Sepal - collection Calyx

Petal - collection coralla

Nectary

Receptacle

Insect and wind pollinators

Colourful bright fragrant petals - Small green absent

Nectar (sucrose ) - No nectar

Anther within flower - Anthers exposed

Stigma within flower - Large feathery exposed

Small quantity sticky heavy pollen - Large quantity light smooth pollen

Male gametes

Pollen grains

Female gametes

Ovule

Tapetum

Nourish developing structure of a mature pollen grain

Anther slides

Epidermis -Fibrous layer

Lateral groove

Pollen sacs (microsporangia)

Tapetum

Vascular strand

Ovary slide

Ovules

Ovary walle

Funicle

Nucellus

Embryo sac

Pollen grain maturation

Pollen mother cells (2n)

Meiosis→

4 Immature pollen grains tetrad (n) each nucleus

Mitosis→ (mature pollen grain)

Tube nucleus (n) (move to tip guide pollen to ovule) → degenerate

Generative nucleus

Mitosis→

• 2 male nuclei (n)

Dehiscence

Opening of anther releasing pollen grains

Pollen mature outer layers dried out tension in lateral goove

Mature pollen grain (n) nucleus

Tube nucleus - guide pollen through style

Generative nucleus - Divide forming 2 male gametes (sperm)

Pollen wall

• Exine tough outer

• Intine thin inner

Ovule structure

Ovule inside ovary

Integuments - Protective layer

Micropyle - Small open for pollen tube entry

Nucellus - Tissue surround embryo sac

Megaspore formation

Megasporocyte (2n) in ovule

Meiosis→

4 haploid megaspores (n)

• Three disintegrate

• One haploid Megaspore

Embryo sac development (after megaspore)

Single megaspore (n) → Mitosis x3 → 8 haploid nuclei

Bottom- 1 egg 2 synergids (n)

Top - 3 antipodal cell

Center - 2 polar nuclei → fuse (2n)

Embryo sac in mature ovule contains

3 antipodals (n)

2 synegrids

1 oosphere (n)

1 polar nucleus (2n)

Synergids (n)

Micropylar end - two

• Attract / guide pollen tube towards egg cell

• Help facilitate fertilisation

Integument

• Protect the ovule

• Later develop into seed coat - testa

Antipodals (n)

Chalazal end

Degenrate - early nutrition

Polar nuclei

Center

Fuse with sperm → triploid endosperm → embryo food

Pollination definition

Transfer pollen grains (anther) to mature stigma of plant of same species

Self-Pollination

Transfer pollen anther to stigma to same flower or plant

Self pollination Advantages and disadvantages

Advantages

• Ensure reproduction when pollinators scarce

• Preserve succesful genomes suited to stable environment

Disadvantages

• Reduce genetic variation - dependant on crossing over meiosis

• Less survival in changing environment

Self pollination adaptions

• Small flower no scent nectar

• Anther close to stigma

• Stigma anther mature same time

Cross pollination definition

Transfer of pollen from anther to stigma of different plant of the same species

Cross pollination advantages and disadvantages

Advantages

• Increased genetic variation → evolution better survival

• Reduce interbreeding - chances of harmful allele combos

Disadvantages

• Depend on pollinators / environment

• Less reliable

Ensuring Cross pollination

• Potandry stamen first potogyny stigma first

• Anther below stigma - pollen wont fall

• Genetic incompatibility

• Separate male female plants

Dichogamy

Anther and stigma mature at different times

Herkogamy

Physical separation of male and female parts

Fertilisation

Fusion of female and male gamete → Zygote

Double fertilisation

2 Male gametes from pollen grain fertilise embryo sac

1. Zygote (2n) → Embryo

2. Triploid endosperm (3n) (foodstore)

Double fertilisation process

1. Pollen tube formation

Pollen grain land on stigma

Tube nucleus direct pollen tube growth through style → ovule

• Enzymes (hydrolases) digest tissue in style

2. Sperm cell

Generative nucleus divide → 2 male gametes (sperm)

Sperm behing in pollen tube)

3. Embryo sac - pollen tube enter through micropyle

4. Fertilisation

1 Sperm cell fuse + EGG → ZYGOTE (2n)

1 Sperm cell fuse + 2 POLAR NUCLEI → TRIPLOID ENDOSPERM (3N)

ZYGOTE → EMBRYO

ENDOSPERM → Nutrition (embryo)

Fruit

Ovule → Seed

Ovary → fruit

Ovary wall become pericarp

• Exocarp - Outer

• Mesocarp - Fleshy middle

• Endocarp - Hard inner surround seed

Types of fruit

Fleshy - Apple tomato → soft mesocarp

Dry - Pea pod almond → Hard pericarp

Seed dispersal

Ensure seed reach suitable environment

Wind - Wing hairs light seeds - Dandelion

Water - Boayant - Coconut

Animals - hooks spines

Ingested - Fleshy fruit - Berries

Bursting - Dry plod splits

Structure Dicot -Vicia faba,

• Hilum - scar where funicle attached

• Micropyle - small pore

• Testa - Outer coat

• Two cotyledons - food storage

• Radicle

• Plumule

Non endospermic

Structure Monocot -Zea mays

• Testa

• Endosperm ( food store)

• Single cotyledon ( scutellum)

• Radicle

• Plumule

• Coleoptile (plumle sheat)

• Plumule

Monocots and Dicots

One cotyledon in seed - Two cotyledons

Leaf veins are parallel - Leaf veins form network

Sepals, petals stamens multiples of 3 - Sepals petals stamen multiples of 4,5

Vascular bundles scattered in stems - In ring in Stems

Vascular bundles Scattered in roots - In centre of roots

Seed survival

• Inhibitors only allow germination in spring ‘ vernalisation’ broken down in cold weather

• Testa protects embryo

• Food store supports early growth

• Ability to remain dormant

• Resistant to desiccation

• Can be dispersed away from parent plant

Seed dispersal reasonings

• Competition light water nutrients

• Overcrowding

• Disease transmission

Why does cross pollination increase genetic variation

• Gametes come from different plants

• Meiosis produces haploid gametes with different allele combinations

• Random fertilisation produces unique offspring

Seed development

• Ovule develops into a seed

• Diploid zygote (2n) divides by mitosis

• Forms diploid embryo

• Embryo consists of plumule, radicle and cotyledon(s)

• Triploid primary endosperm nucleus (3n) divides by mitosis

• Forms endosperm tissue (food store)

• Integuments develop into testa

• Micropyle remains as a pore in the testa