Sexual Reproduction In Flowering Plants

Question 1

Asexual reproduction

Answer 1

Involves only one parent

Question 2

Sexual reproduction

Answer 2

Involves the union of two sex cells (gametes)

Question 3

Why is Meiosis essential for sexual reproduction

Answer 3

It is needed to halve the chromosome number in the formation of gametes

Question 4

Zygote

Answer 4

A zygote is a diploid cell, which is made by two gametes fusing together

Question 5

Gametes

Answer 5

Haploid cells capable of fusion

Question 6

Advantage of sexual reproduction

Answer 6

It shows variation due to the mixture of genes form the two parents, which is the basis of evolution

Question 7

Receptacle

Answer 7

Part of the flower from which flowering parts arise

Question 8

Sepals

Answer 8

Brown leaf-like structures which protected the flower when it was a bud. (Originally green)

Question 9

Petals

Answer 9

Are large and brightly colored to attract animals, which help pollinate other flowers. (Usually insects are attracted to them)

Question 10

Stamens

Answer 10

Male parts of the flower.
Consists of a thin stalk that contains a vascular bundle to bring food and water to the anther. Then anther produces pollen grains as a result of meiosis

Question 11

Carpels

Answer 11

Female parts of the flower. 
Three parts: 
Stigma - where the pollen lands
Style - through which the pollen tube grows. 
Ovary - contains one or more ovules.

Question 12

Describe male gamete formation.

Answer 12

Meiosis takes place in some of the cells lining he inside of the anther to produce pollen grains containing a single haploid nucleus.
Each pollen grain divides to form male sex cells. When they pollen grains are fully developed, the anther splits so that the pollen grains are exposed

Question 13

Structure of pollen sacs

Answer 13

4 pollen sacs in an anther.

Each one enclosed by a protective epidermis and fibrous layer.

Question 14

Pollen grain development

Answer 14

Diploid microspore mother cells are in each pollen sac. They divide to produce a cluster of 4 haploid cells called tetrad. Each break up to form 4 separate haploid pollen grains (microspores). Each microspore divides to produce 2 haploid nuclei. The tube nucleus forms the pollen tube and then will degenerate. The generative nucleus divides to form male gametes.

Question 15

Exine

Answer 15

The thicker outer wall of a pollen grain.

It is made of a very durable material that allows it to survive for long periods of time.

Question 16

Intine

Answer 16

A thin, inner coat on a pollen grain.

Question 17

Pollen grain

Answer 17

Not gametes. They are not involved in fertilization.

They only form the male sperm nuclei, which are the gametes.

Question 18

Embryo sac

Answer 18

A diploid cell that divides by meiosis to form a single haploid cell.
The embryo sac then undergoes mitosis three times to form eight haploid nuclei.
Out of the eight, five die. The others are the egg cell and the two polar nuclei.

Question 19

Integuments

Answer 19

Walls in the ovule.

They have a small opening called the micropyle, through which a pollen tube can enter.

Question 20

Megaspore mother cell

Answer 20

A diploid nucellus cell that supply’s nutrients to the ovule.
Located low down in the ovule.
This cell divides by meiosis to form 4 haploid cells, three of which degenerate and die off. The remaining cell is called the embryo sac

Question 21

Pollination

Answer 21

The transfer of pollen from an anther to a stigma of a flower from the same species.

Question 22

Self pollination

Answer 22

Involves the transfer of pollen from an anther to a stigma on the same plant.
An extreme form of inbreeding. The resulting seeds of self pollination may be less sturdy and vigorous.

Question 23

Cross pollination

Answer 23

Involves the transfer of pollen from an anther to a stigma on a different plant.

Question 24

Methods of pollination

Answer 24

Wind and animals

Question 25

Wind pollination.

Answer 25

A very wasteful of pollen.
Plants that use wind pollination have large amounts of pollen, large anthers, stigmas that are large and small unattractive petals.
E.g. grass, oaks, hazel

Question 26

Animal pollination

Answer 26

More advanced form of pollination. More precise in carrying pollen directly to a stigma and less pollen is wasted.
Large attractive, scented petals, small amounts of heavy large sticky pollen, small anthers

Question 27

Fertilization

Answer 27

The union of the male and female gametes to form a diploid zygote.

Question 28

Double fertilization

Answer 28

When one sperm nucleus joins with an egg nucleus to form a diploid zygote. This zygote will develop into an embryo.
The second sperm nucleus joins with the two nuclei to form a triploid endosperm nucleus.

Question 29

Radicle

Answer 29

The part of the plant embryo that develops into a root.

Question 30

Plumule.

Answer 30

The part of the plant embryo that develops into the shoot.

Question 31

Cotyledon

Answer 31

A seed leaf

Question 32

Non endospermic seed

Answer 32

Has no endosperm when fully formed.

Question 33

Endospermic seed

Answer 33

Contains some endosperm when fully formed

Question 34

Seed formation

Answer 34

He fertilized ovule becomes the seed.
The zygote grows repeatedly by mitosis that forms a group of cells that give rise to the embryo.
At the same time the endosperm nucleus divides repeatedly to produce many endosperm cells. The endosperm acts as a good store. E.g oils, protein, starch

Question 35

Embryo

Answer 35

Consists of the future root (radicle), and the future shoot (plumule)

Question 36

Fruit

Answer 36

A developed ovary

Question 37

Monocot and do it seeds

Answer 37

Monocots are plants in which the seed has only one cotyledon.
Dicots have two cotyledons in each seed.

Question 38

Food storage.

Answer 38

In monocots food is stored in the endosperm.
The growing embryo absorbs food stored in the endosperm.
Meanwhile in dicots, food is stored in the cotyledons.

Question 39

Fruit formation

Answer 39

As a seed is developing, the ovary becomes the fruit. The process of fruit formation is stimulated by growth stimulators produced by the seed.
Fruits protect the seed and help in its dispersal.

Question 40

Parthenocarpy

Answer 40

The development of seedless fruits. This is a form of virgin birth, when the egg is not fertilized.

Question 41

Seedless fruits

Answer 41

Some arise genetically (naturally or by special breeding programmed) e.g bananas
Another way is to spray plants with growth regulators. E.g cherries, peaches

Question 42

Dispersal.

Answer 42

The transfer of a seed or fruit away from the parent plant.

Question 43

Seed dispersal

Answer 43

The main methods are wind, water, animal and self-dispersal

Question 44

Wind dispersal

Answer 44

Examples are orchids, dandelions and sycamore. Each have different adaptations to help carry them through the wind. E.g. small, light, wings.

Question 45

Water dispersal

Answer 45

Coconut trees, alders and water lilies. They have light, air filled fruits that float which allows them to be transported by streaks and rivers

Question 46

Animal dispersal

Answer 46

Very successful as animals can carry seeds and fruits long distances. Fruits dispersed by animals usually have either of the two major adaptations. Sticky fruits and edible fleshy fruits.

Question 47

Sticky fruits

Answer 47

Have hooks called burrs to cling onto animal’s hair to be carried away.

Question 48

Edible, fleshy fruits

Answer 48

They attract animals. Animals eat and digest the fruit, the seed passes through the intestine unharmed and then the seed is released with the farces.

Question 49

Self dispersal.

Answer 49

Some fruits have explosive mechanisms that catapult the seeds away.

Question 50

Dormancy.

Answer 50

A resting period when seeds undergo no growth and have reduced cell activity or metabolism.

Question 51

How is dormancy brought about?

Answer 51

• Growth inhibitors may delay growth until they are broken down by water, cold or decay.
• the tests may be impermeable to water or oxygen. Eventually the tests breaks down allowing water and oxygen to enter the seed.
• the testa may be too tough to allow the embryo to emerge.

Question 52

Dormancy I’m agriculture and horticulture

Answer 52

Special conditions may be necessary to break dormancy in seeds before they are planted.

Question 53

What are the conditions necessary to break dormancy in seeds.

Answer 53

• Soaking the seeds in water.
• Physical damage
• exposing the seed to light or dark.
• exposing the seed to cold temperatures.

Question 54

Advantages of dormancy

Answer 54

• avoid harsh conditions in winter.
• gives the embryo time to fully develop
•Provides time for the seed to be dispersed.
• Maximizes the growing season young seeds.
Helps the survival of the species.

Question 55

Germination

Answer 55

The regrowth of the embryo, after a period of dormancy, if the environmental conditions are suitable.

Question 56

Conditions necessary for germination

Answer 56

• water is needed to allow enzyme reactions to occur. It causes the seed to swell and allows enzymes to function.
• oxygen for aerobic respiration. Absorbed from the soil.
• A suitable temperature is needed to allow enzyme reactions to take place. (Between 5 and 30 degrees)
• dormancy must be completed

Question 57

Events in germination

Answer 57

• Begins when the seed absorbs water through the testa. This allows enzyme activity
• in germinating seeds, oils are digested to fatty acids and glycerol, starch is digested to glucose and proteins are disgusted to amino acids.
•products of digestion are moved through embryo.
• cell walls and enzymes are made.
• the fats and some of the glucose are used in respiration to produce energy.
• mass of the seed falls.
• as the weight of the food stores falls, the weight of the embryo increases.
The radicle bursts through testa.
• plumule emerges above ground and leaves are made.
• photosynthesis starts and the mass of the seedling increases.

Question 58

Changes in the dry weight (mass) of germinating seeds.

Answer 58

• mass = weight without water.

* measures by placing plant in oven at 100 degrees until the weight remains constant.

Question 59

Stages in seedling growth:

Cotyledons remain below soil (broad bean example)

Answer 59

• the seed absorbs water, enzymes become active and the radicle grows.
• radicle bursts out through the testa and grows down (geotropism).
• the plumule emerges.
• plumule grows through the soil and it’s delicate leaves are protected by the plumule being hooked over.
• the cotyledons shrivel as good is transferred form them.
• the radicle develops into the primary root, which forms many side roots.
• the plumule straightens up and produces the first true leaves.

Question 60

Stages of seedling growth:

Cotyledons move above the soil. (Sunflower seed example)

Answer 60

• cotyledons are forced above the soil.
• once above the soil, the fruit wall falls to the ground. The cotyledons open out, become green and photosynthetic. Plumule emerges from between the cotyledons and forms the first true leaves.