Rep plants part 3

1. Plant
Reproduction
PART III

2. 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.

3. 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.

4. 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

5. Pollination and fertilization in flowers
• Video

6. 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.

7. 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.

8. 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

9. 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

10. 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

11. 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.

12. 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

13. 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

14. Homework
• Page 211 Q. 4 and 5