Plant Reproduction

PART III

Last Lesson Review• 16.13 What is the function of a flower?• Sexual Reproduction• 16.14 In which part of the flower are male gametes made?• Anthers• 16.15 In which part of the flower are female gametes made?• Ovules• 16.16 What is pollination?• The transfer of pollen grains from male part to female part of the flower• 16.17 Why do wind-pollinated flowers usually produce more pollen than

insect-pollinated flowers?• A lot of the pollen is wasted and will not land on the female stigma.

Pollination and fertilization in flowers• Fertilization• Pollination is when pollen grain transfers from stamen to carpel• In order for fertilization to occur: - the male gamete (inside the pollen

grain) must reach the female gamete (inside the ovule, which is inside the ovary)• This is achieved via a pollen tube. The pollen grain grows this tube,

secreting enzymes to digest through the style.

Pollination and fertilization in flowers• Fertilization• The ovule is surrounded by layers of cells, integuments. At one end is

a hole called micropyle. The pollen tube grows through the micropyle.• The nucleus of the male gamete now travels down the pollen tube

and into the ovule. Fusing with the female gamete. Fertilization has now occurred.

• Integument = layers of cells surrounding the ovule• Micropyle = hole in the integument, in which the pollen tube passes

• NB. One pollen grain for one ovule

Pollination and fertilization in flowers• Video

Pollination and fertilization in flowers• Seeds• After fertilization, parts of the flower no longer needed will fall off

(stamens, petals, sepals) their job has been completed• After fertilization, each ovule contains a zygote.• This zygote divides by MITOSIS, forming an embryo.• The ovule with embryo = SEED.

• Integuments become hard and dry to protect. Water is removed so the seed becomes dormant.

Pollination and fertilization in flowers• Seeds• Parts of the seed.• Radicle – grows into the root• Plumule – grows into the shoot• Radicle + Plumule = Embryo• Testa – the hard, dry integuments• Hilium – scar where seed was attached to the ovary• Cotyledons – food storage • Micropyle – hole in which water can enter

• The ovary also grows. Forming fruit.

Questions• 16.18 After pollination, how does the male gamete reach the ovule?• Through a pollen tube that grows from the pollen grain through the style.• 16.19 What is the micropyle?• A hole between the integuments of the ovule, through which the pollen tube

grows.• 16.20 What happens to the following once a flower's female gametes have been

fertilized?• Petals?• Stamens?• Zygote?• Ovule?• Integuments?• Ovary?

• They fall off• They fall off• Develops into embryo• Develops into seed, containing the embryo• Develop into testa (seed coating)• Develops into fruit

Conditions that affect germination in plants• Remember water is removed from a seed so that it remains dormant (dehydrated)• No water = no metabolic reactions

• This is useful because seeds can survive difficult conditions (cold/drought)

• When seed gains water, it enters through the micropyle. Water makes the cotyledons swell. Eventually the cotyledons burst the testa.

• Once sufficient water, enzymes in cotyledons become active:• Amylase breaks down starch into maltose• Protease breaks down protein into amino acids

• Maltose and Amino acids dissolve in water, diffuse to the embryo for use as food

Conditions that affect germination in plants

Water enters seed through

micropyle

Cotyledons swell with

water

Cotyledons eventually

burst the testa

Sufficient water activates

enzymes in cotyledons

Amylase, starch to maltose

Protease, protein to

amino acids

Maltose/amino acids dissolve

in water

Diffuses to embryo, used as food to grow

Questions• 16.21 What do the cotyledons of a seed contain?• Starch and Protein• 16.22 What does dormant mean?• Inactive, metabolism slowed down, practically stopped• 16.23 What is the advantage of seed dormancy?• Allows seed to survive harsh conditions• 16.24 What activates the enzymes in the cotyledons?• The intake of water• 16.25 What do the enzymes do?• Break down starch and protein reserves so embryos can use them as

food to grow.

Comparing Sexual and Asexual Reproduction• Many plants use both• Asexual – parent cells divide by mitosis = genetically identical clones• No genetic variation

• Sexual – parent cells divide by meiosis, forming gametes (contain half the chromosomes of a normal cell)• When two sets of chromosomes from two gamete cells fuse,

fertilization. A new combination of chromosomes is created.• Genetic variation. Genetically different offspring

Comparing Sexual and Asexual Reproduction• Advantages of Asexual Reproduction• Offspring gain same adaptations to an environment• Doesn't need to wait to be pollinated (isolated areas)• Farmers can propagate many plants with the same traits

• Advantages of Sexual Reproduction• Asexual reproduction cannot produce offspring that might be resistant

to a new disease• Pollen is dispersed over large areas, reducing competition• Farmers can produce new varieties

Homework• Page 211 Q. 4 and 5