Sexual reproduction in plants

Label this diagram

1. stigma

2. style

3. ovary

4. anther

5. filament

6. petal

7. sepal

8. peduncle

Label this diagram

1. stigma

2. style

3. anther

4. filament

5. petal

Which structures make up the stamen?

• anther

• filament

Which structures make up the carpel?

• ovary

• ovule

• style

• stigma

What is the receptacle?

top of flower stalk from which different parts of the flower develop

Which structure makes up the calyx?

sepals

Which structure makes up the corolla?

petals

What is the calyx?

• first set of modified leaves → sepals

• protect flower while it’s still forming and before flower bud opens

What is the corolla?

• layer of modified leaves → petals

• often large, coloured and patterned → attracts insects

  • some colours (e.g. UV) only visible to insects

What is the stamen?

• made of filament and anther

  • filament carries water and nutrients to anther in vascular bundle

• male reproductive organ

  • site of mitosis and meiosis to produce male gametes

What is the carpel?

• composed of ovary, style and stigma

  • ovary is site of meiosis to produce female gametes → contained in ovules

  • following fertilisation, ovules becomes seeds

  • style supports stigma

  • stigma is sticky surface that pollen grain land on

• female reproductive organ

What is the nectary?

• may also be present at base of stamens

• secrete sweet substance (nectar) that attracts insects → carry pollen from one flower to another

Define solitary flowers

only one flower on a stem

Define inflorescence

many flowers on one stem

Define hermaphrodite

flowers with both female and male parts

Define monoecious

separate male and female flowers on plants

Define dioecious

separate male and female plants

Identify the kind of plant shown and label the diagram

wind pollinated plant

1. anther

2. stigma

3. petals

How does the size and colour of petals in wind pollinated plants and insect pollinated plants differ?

• wind pollinated:

  • small, dull-coloured

  • less attractive flower

• insect pollinated

  • big, visible and scented flower

  • brightly coloured → attracts insects

How does the appearance of stamens in wind pollinated plants and insect pollinated plants differ?

• wind pollinated

  • long stamen

  • usually sticks out of petals

• insect pollinated

  • short stamen

  • hidden within the petals

How does the appearance of anthers in wind pollinated plants and insect pollinated plants differ?

• wind pollinated

  • big and sticks loosely at tip of filament

• insect pollinated

  • small and sticks firmly at tip of filament

How does the appearance and texture of pollen in wind pollinated plants and insect pollinated plants differ?

• wind pollinated

  • tiny, smooth and light

  • numerous

• insect pollinated

  • big, coarse and spiky

  • few in number

How does the appearance of styles in wind pollinated plants and insect pollinated plants differ?

• wind pollinated

  • long and hairy

• insect pollinated

  • short and sticky

  • even stigma

How does the nectar in wind pollinated plants and insect pollinated plants differ?

• wind pollinated

  • doesn’t produce nectar

• insect pollinated

  • sweet nectar

What are some examples of wind pollinated plants?

maize, grass, paddy and wild grass

What are some examples of insect pollinated plants?

rose, hibiscus, orchid, durian

Define self-pollination

pollen from anther of a flower is transferred to mature stigma of the same flower or another flower on the same plant

Define dichogamy

when the stamen and stigma ripen at different times

What are the 2 types of dichogamy?

• protandry → stamen ripens before stigma

• protogyny → stigma ripens before stamen (rarer)

How is self pollination prevented?

• anther below stigma so pollen can’t fall onto it

• genetic incompatibility → pollen can’t germinate on stigma of flower from which it was produced

• separate male and female flowers on plants (maize) → monoecious

• separate male and female plants (holly) → dioecious

• dichogamy → anther and stigma develop at different times

Why should self-pollination be avoided?

• prevent inbreeding

• cross-pollination leads to an increase in genetic variation

• prevent homozygosity → could result in recessive traits

• cross pollination results in larger gene pool

  • increases chance of survival/selective advantage

Why could self-pollination be advantageous?

preserves successful genomes that are suited to relatively stable environment

Identify this structure and label the diagram

anther

1. line of dehiscence

2. vascular bundle

3. pollen sac

4. tapetum

5. epidermis

Where are the male sex cells found?

• anther

• inside pollen sacs surrounded by tapetum

What is the function of the tapetum?

inner cell walls that provide nutrients to the developing pollen grains

What is dehiscence?

the opening of the anther, releasing pollen grains

What is the first stage in the development of the male gamete?

• diploid mother cells in pollen sacs undergo meiosis

• each forms a tetrad → contains 4 haploid cells which become 4 pollen grains

What is the second stage in the development of the male gamete?

• haploid cells undergo mitosis

• each form a pollen grain with 2 haploid nuclei

  • tube nucleus

  • generative nucleus

What is the third stage in the development of the male gamete?

• cell wall thickens → mature pollen grain formed

What is the function of the cell wall in male gamete and what are the 2 layers of this cell wall called?

• prevents desiccation (drying out) of the pollen grain

• intine (inner layer) and exine (outer layer)

What is the function of the generative nucleus?

divides by mitosis to form 2 male nuclei during pollination

Identify this structure and label the diagram

immature plant ovule

1. nucellus

2. mother cell (2n)

3. integuments

4. funicle

5. megaspore mother cell

What is the function of the nucellus?

to provide nutrition to the developing embryo

What is the first stage in the development of the female gamete?

megaspore mother cell undergoes meiosis making 4 haploid cells → 3 degenerate

What is the second stage in the development of the female gamete?

remaining cell undergoes 3 rounds of mitosis → produces 8 haploid nuclei (one of these is the female gamete)

What is the third stage in the development of the female gamete?

• 2 of haploid nucleus fuse to form polar nuclei

• remaining nuclei develop cytoplasm around themselves and become separated by cell walls

What is the final structure of the ovule once the female gamete has been developed and the polar nucleus has been formed?

• 3 antipodal cells → top of ovule

• 2 polar nuclei → middle

• 2 synergids → on either side of female gamete

• female gamete → bottom of ovule

What happens in the 1st stage of double fertilisation?

• pollen grain adheres to stigma

• contains 2 cells → generative nucleus and tube nucleus

What happens in the 2nd stage of double fertilisation?

• pollen tube cell grows into style

• generative cell travels inside pollen tube

• divides to form 2 male gametes

What happens in the 3rd stage of double fertilisation?

pollen tube penetrates opening in ovule → micropyle

What happens in the 4th stage of double fertilisation?

• one male gamete fertilises female gamete → forms diploid zygote

• other male gamete fertilises 2 polar nuclei → forms triploid endosperm

What is the function of the endosperm?

to provide nutrition for developing embryo

What happens to the diploid zygote after fertilisation?

divides by mitosis to form an embryo

Which structures are contained in the embryo?

• plumule (developing shoot)

• radicle (developing root)

• one or two cotyledons

What is the micropyle?

pore in the seed

What do the integuments become after fertilisation?

become seed coat/testa (dried out with lignin)

What does the ovule contain and what does it become after fertilisation?

• contains endosperm, embryo and testa

• becomes seed

What happens to the funicle after fertilisation?

attaches to hilum

What does the ovary become after fertilisation?

fruit

What is a dicotyledon?

• 2 seed leaves (cotyledons)

• endosperm absorbed into cotyledons so non-endospermic

What is a monocotyledon?

• 1 seed leaf (cotyledon)

• endosperm remains as food source

• ovary wall and testa fuses

What does hypogeal mean?

below ground germination

What does epigeal mean?

above ground germination

What is the plumule?

shoot

What is the radicle?

root

Identify the type of seed and label the diagram (beautiful ik)

monocotyledon

1. testa and ovary wall fused

2. endosperm

3. coleoptile (plumule sheath)

4. plumule

5. radicle

6. cotyledon

7. funicle

Identify the type of seed and label the diagram

dicotyledon

1. ovary wall

2. plumule

3. funicle

4. position of micropyle

5. radicle

6. cotyledon

7. testa

What happens during epigeous germination?

• radicle emerges from seed, raising cotyledons and remains of seed coat above ground

• cotyledons expand → may function as normal photosynthetic leaves but can transfer remaining nutrients to seedling and degenerate instead

What happens during hypogeous germination?

• cotyledons don’t emerge from seed

• force radicle and plumule out of seed

• cotyledons remain underground and transfer nutrients to developing root and shoot

What are the differences between monocotyledons and dicotyledons?

• monocotyledons

  • sprout with 1 leaf

  • parts with multiples of 3

  • veins parallel to leaves

  • vessels scattered

  • pollen has single pore

  • grasses, lilies, palms

• dicotyledons

  • sprout with 2 leaves

  • parts with multiples of 4/5

  • veins branch out

  • concentric rings of vessels

  • pollen has 3 pores

  • apples, sunflowers, strawberries

How has the evolutionary development of seeds aided the survival of angiosperms?

• low metabolic rate in dormant seeds → survive very cold weather

• testa chemically resistant → seeds survive adverse chemical conditions

• water content of dormant seeds reduced below 10% → can survive very dry conditions

• testa physically protects embryo

• endosperm or cotyledons provide nutrients → lasts until seed can photosynthesise

• seeds dispersed great distances from parent → no competition

• dispersal allows colonisation of new habitats

What conditions are necessary for germination?

• suitable temperature

  • optimum for enzymes involved → between 5°C - 30°C

• light

  • only some species

• water

  • to make cells turgid → testa bursts

  • to mobilise enzymes

  • to hydrolyse food reserves

  • to transport dissolved substances to embryo

• oxygen

  • anaerobic respiration to release energy

Why does stored food need to be hydrolysed?

insoluble so can only be used by embryo for protein synthesis and respiration if hydrolysed

What are the food reserves of the seed?

• endosperm/cotyledons

• starch → main reserve

• oils

• protein

What is the process of germination in monocotyledons?

• water enters seed through micropyle

• Gibberellic acid (plant growth regulator) diffuses from embryo to Aleurone layer → has high protein content

• Gibberellic acid triggers the transcription of genes

• translation of mRNA results in production of enzymes (incl. protease and amylase)

• protease hydrolyses protein stores, releasing amino acids that are used in amylase production

• amylase hydrolyses starch in endosperm

• Maltose and glucose diffuse to embryo plant where they’re used in respiration → produce ATP needed for cell division and synthesis of organic molecules

What is the process of germination in dicotyledons?

• water imbibed through micropyle

• tissues swell and enzymes become more active

• food reserves hydrolysed

• amylase digests starch in cotyledons into maltose

• maltose → glucose by maltase

• proteins → amino acids by protease

• transported to embryo

• glucose used for aerobic respiration and converted to cellulose for cell wall synthesis

• amino acids used for synthesis of proteins

• proteins used for mitosis/growth of plumule and radicle