B10.2 : Sexual reproduction in plants

Question 1

Pollination

Answer 1

1. Pollination is the transfer of pollen grains from the male anther to the female stigma.
2. Bees are important insect pollinators
3. e.g. Dandelions are wind-pollinated

Question 2

Types of pollination

Answer 2

1. Self-pollination

2. Cross-pollination

Question 3

Fertilisation

Answer 3

1. After pollination, a structure called a pollen tube grows out of the pollen grain down the style.
2. The male gamete travels down the pollen tube to the ovule inside the ovary.
3. Fertilisation is when the nucleus of a male gamete fuses with the nucleus of a female gamete (the ovule).
4. After fertilisation the petals, stamen and sepals fall off. The ovule turns into a seed, the fertilised egg inside develops into an embryo plant.

Question 4

Cross-pollination

Answer 4

1. Cross-pollination is the transfer of pollen from the anthers of one flower to the stigma of a flower on a different plant.
2. This introduces genetic variation into the offspring, so they are more able to respond to environmental changes.

Question 5

Self-pollination

Answer 5

1. Self pollination happens when pollen from an anther is transferred to the stigma of the same flower, or a different flower on the same plant.
2. The offspring produced are identical to the parent plant, so a disadvantage of this is a lack of genetic variation in the offspring.
3. An advantage of this is that if a plant is not able to reproduce by cross-pollination (for example there are no pollinators nearby), they can still reproduce through self-pollination.

Question 6

Stages of reproduction in flowers

Answer 6

1. pollination

2. fertilisation

Question 7

Pollination Methods

Answer 7

1. Insect-pollinated flowers
2. Insect-spread pollen
3. Wind-pollinated flowers
4. Wind-spread pollen

Question 8

Insect-pollinated flowers

Answer 8

1. Some plants rely on insects to carry pollen between flowers.
2. These plants often have large, brightly-coloured petals and also produce sweet nectar to attract insects.
3. Insects brush past the anthers as they try to get to the nectar, and become covered in pollen, which is transferred to the next flower the insect visits.

Question 9

Insect-spread pollen

Answer 9

This pollen is barbed so that it attaches easily to insects that brush past the anthers.

Question 10

Wind-pollinated flowers

Answer 10

1. These flowers rely on gusts of wind to carry their pollen to other flowers.
2. They do not produce nectar and don’t have large or brightly-coloured petals.
3. The stigmas are large and extend out of the flower so they can catch any passing pollen.
4. No scent or nectary

Question 11

Wind-spread pollen

Answer 11

1. These pollen grains are smooth and lightweight so that they can be carried by the wind over long distances.
2. Some may also have wing-like structures so that they are picked up by the wind easily.

Question 12

Germination

Answer 12

After fertilisation, seeds need certain environmental conditions in order to germinate (sprout roots and shoots)

Question 13

Germination conditions

Answer 13

1. Water
2. Oxygen
3. Suitable temperature

Question 14

Water

Answer 14

Seeds are often dehydrated, so need water to rehydrate to start germination, but not too much water as they might rot.

Question 15

Oxygen

Answer 15

Seeds need oxygen for respiration

Question 16

Suitable temperature

Answer 16

Seeds need to be a suitable temperature so that their enzymes can work well in germination

Question 17

Female and male flower sex organ

Answer 17

1. The anther and the filament make up the stamen (the flower’s ‘male’ sex organ).
2. The stigma, style, ovary and ovules make up the carpel (the flower’s ‘female’ sex organ).
3. Most flowers have both stamens and carpels.
4. The sepal protects the flower bud when it is developing.

Question 18

Structure of a flower

Answer 18

1. Anther
2. Filament
3. Petal
4. Sepal
5. peduncle
6. Stigma
7. Style
8. Ovary
9. Ovule
10. Receptacle

Question 19

Anther

Answer 19

1. Part of the stamen which is the flower’s male sex organ

2. Produces pollen

Question 20

Ovule

Answer 20

1. Found in the ovary

2. Part of the carpel which is the flower’s female sex organ

Question 21

Petals

Answer 21

1. It’s colourful and scented to attract insects

2. In wind-pollinated flowers it is absent or very small so its hard to be seen

Question 22

nectaries

Answer 22

1. Only in insect-pollinated flowers
2. Absent in wind-pollinated flowers
3. The are used to make nectar which is a sugary liquid food for pollinating insects

Question 23

Stamens

Answer 23

1. In insect-pollinated flowers, it is usually short filaments where the anthers attached firmly to filaments; inside the flower for insects to rub against.
2. In wind-pollinated flowers, it has Long filaments so anthers hang outside the flower; anthers loosely attached to the filaments so pollen is easily blown away.

Question 24

Pollen

Answer 24

1. In insect-pollinated flowers, Small quantities of sticky, spiky pollen grains that stick easily to insects’ bodies
2. In wind-pollinated flowers, there are Large quantities of smooth, light pollen that can easily be carried by the wind.

Question 25

Carpels

Answer 25

1. In insect-pollinated flowers, carpels are sticky, small stigmas usually inside the flower for insects to rub against.
2. In wind-pollinated flowers, carpels are large, feathery stigmas to catch pollen grains in the air