Sexual reproduction in Plants

Question 1

What is the name for plants that have flowers?

Answer 1

Angiosperms.

Question 2

What are the male spores of plants?

Answer 2

Pollen grains, produced in the anther.

Question 3

What are the female spores of plants?

Answer 3

Embryo sacs, produced in the ovule in the ovary.

Question 4

What is a hermaphrodite?

Answer 4

Flowers that contain both male and female parts.

Question 5

How is a flower defined?

Answer 5

Four sets of modified leaved arising from a receptacle at the base.

Question 6

What does the stamen (male part) consist of?

Answer 6

The anther and filament.

Question 7

What does the carpel (female part) consist of?

Answer 7

The stigma, style, ovary, ovule and embryo sac.

Question 8

What are sepals?

Answer 8

Found in the calyx, they are usually green and protect the flower in the bud.

Question 9

What is the function of the nectary?

Answer 9

It releases sweet smelling nectar to attract pollinators.

Question 10

What is the function of the filament?

Answer 10

It supports the anther and transports sucrose, minerals and water to the developing pollen grain.

Question 11

What is the function of the anther?

Answer 11

It produces pollen grains.

Question 12

What is the function of the stigma?

Answer 12

It is the receptive surface for the pollen grains.

Question 13

What is the function of the style?

Answer 13

It supports the stigma.

Question 14

What is the function of the ovary?

Answer 14

It produces embryo sacs.

Question 15

Describe the features of insect-pollinated flowers

Answer 15

Colourful petals, sometimes with nectar guides
Scent and nectar
Anthers within the flower
Stigma within the flower
Small quantities of sticky, sculpted pollen
Produces larger pollen grains

Question 16

Describe the features of wind-pollinated flowers

Answer 16

Petals absent or small, green and inconspicuous
No scent or nectar
Anthers hanging outside the flower
Large, feathery stigma hanging outside the flower
Large quantities of smooth pollen
Produces smaller pollen grains

Question 17

What does the anther consist of?

Answer 17

Vascular strand, tapetum, pollen sac and a lateral groove.

Question 18

What does a pollen grain consist of?

Answer 18

Exine, intine, generative and tube nucleus.

Question 19

Describe pollen grain development

Answer 19

Each diploid mother cell undergoes meiosis, forming a tetrad of four haploid cells. Each haploid cell undergoes mitosis to produce two nuclei, a generative and a tube nucleus.

Question 20

What is the function of the tapetum?

Answer 20

It provides nutrients and regulatory molecules to the developing pollen grains. It also forms the cell well, which is tough and resistant to chemical, desiccation resistant and resistant to mutation.

Question 21

What happens when the pollen grain is mature?

Answer 21

The outer layers of the anther dry out, causing tension in the lateral groove. Dehiscence occurs in which the tension pulls the walls of the anther apart and the edges of the pollen sacs curl away. An opening called the stomium exposes the pollen grains and they are carried away by the wind.

Question 22

Describe embryo sac development

Answer 22

In each ovule, a megaspore mother cell undergoes meiosis, making four haploid cells. Three disintegrate and the remaining cell undergoes three round of mitosis, producing eight haploid nuclei. These nuclei fuse to produce one haploid oosphere, three haploid antipodals, two haploid synergids and a diploid polar nucleus.

Question 23

What does a mature embryo sac consist of?

Answer 23

One haploid oosphere, three haploid antipodals, two haploid synergids and a diploid polar nucleus.

Question 24

What is pollination?

Answer 24

The transfer of pollen grains from the anther to the mature stigma of a plant of the same species.

Question 25

What is self-pollination?

Answer 25

The pollen from the anthers of a flower is transferred to the mature stigma of the same flower of another flower of the same plant.

Question 26

What is cross-pollination?

Answer 26

The pollen is transferred from the anthers of one flower to the mature stigma on another flower on another plant of the same species.

Question 27

What are the advantages of self-pollination?

Answer 27

Inbreeding can preserve a successful genome that is suitable in a relatively stable environment.

Question 28

What are the disadvantages of self-pollination?

Answer 28

There is a greater chance of two potentially harmful recessive alleles being brought together Less genetic variation

Question 29

What are the advantages of cross-pollination?

Answer 29

Outbreeding reduces the chance of producing harmful allele combinations Outbreeding is of great evolutionary significance as in a particular environment, some genomes are more successful than others. It may allow species to survive in a changing environment More genetic variation

Question 30

What are the different methods employed to ensure cross-pollination?

Answer 30

Dichogamy- where the stamen and stigma ripen at different times The anther being below the stigma so pollen cannot fall onto it Genetic incompatibility Separate male and female flowers on the same plant Separate male and female plants

Question 31

What is fertilisation?

Answer 31

The process by which a male gamete fuses with a female gamete to produce a zygote.

Question 32

Describe the steps of double fertilisation

Answer 32

1. When a compatible pollen grain lands on the stigma, it germinates in the sucrose solution secreted by the stigma and produces a pollen tube. 2. The pollen tube nucleus is at the tip of the tube, with two male nuclei behind. 3. The pollen tube grows out of the pollen grain through a gap in the cell wall and down the style, up a gradient of chemo attractants. The pollen tube nucleus uses hydrolases to digest the tissues of the style. 4. The pollen tube grows through a gap in the integuments, the micropyle and passes into the embryo sac. 5. The pollen tube nucleus disintegrates. 6. The tip of the pollen tube opens, releasing two male gametes into the embryo sac. 7. One of the male gametes fuses with the oosphere to form a diploid zygote. 8. The other male gamete fuses with the diploid polar nucleus to make a triploid endosperm nucleus.

Question 33

Describe the ovary in a plant

Answer 33

Nuclei in the embryo sac are surrounded by the nucellus, a layer of cells which provide nutrients. Around the nucellus are two layers of cells called integuments. A gap in the integuments is called the micropyle.

Question 34

What does the diploid zygote become after fertilisation?

Answer 34

It divides by mitosis, becoming an embryo consisting of a plumule (shoot), a radicle (root) and one or two cotyledons (seed leaves).

Question 35

What does the triploid endosperm nucleus become after fertilisation?

Answer 35

It develops into a food store, providing food for the developing embryo.

Question 36

What do the outer integuments become after fertilisation?

Answer 36

They dry out, harden and become waterproof with deposits of lignin and become the seed coat or testa.

Question 37

What does the micropyle become after fertilisation?

Answer 37

It remains as a pore in the seed.

Question 38

What does the ovule become after fertilisation?

Answer 38

It becomes the seed.

Question 39

What does the funicle become after fertilisation?

Answer 39

It becomes the funicle of the seed, attached at the hilum.

Question 40

What does the ovary become after fertilisation?

Answer 40

It becomes the fruit.

Question 41

Describe monocots

Answer 41

One cotyledon in seed Leaf veins are parallel Sepals, petals and stamens are in multiples of three Vascular bundles scattered in roots Vascular bundles scattered in stems

Question 42

Give an example of a monocot

Answer 42

Maize.

Question 43

Describe dicots

Answer 43

Two cotyledons in seed Leaf veins form a network Sepals, petals and stamens are in multiples of four or five Vascular bundles in the centre of roots Vascular bundles in a ring in stems

Question 44

Give an example of a dicot

Answer 44

Broad bean.

Question 45

What does dormant mean?

Answer 45

It describes a seed when its active growth is suspended as germination can only occur when specific conditions are met.

Question 46

What is seed dispersal?

Answer 46

The movement of seeds away from the parent plant.

Question 47

Why is seed dispersal neccassary?

Answer 47

If a seed were to germinate close to a parent plant, the parent plant would be more successful at obtaining water and minerals from the soil, and cast a shadow over the seedling, outcompeting it.

Question 48

Describe and give an example of a plant with a wind dispersal method

Answer 48

Sails that allow wind dispersal, stiff parachute of hairs or pores. For example, a dandelion seed.

Question 49

Describe and give an example of a plant with a transport dispersal method

Answer 49

Birds eat seeds that pass throw the digestive system and are dispersed in the faeces. For example, a song thrush eating berries.

Question 50

Describe and give an example of a plant with a rolling dispersal method

Answer 50

When the fruit breaks open, the seed falls and rolls away from the parent tree. For example, a horse chestnut fruit.

Question 51

Describe and give an example of a plant with a bursting dispersal method

Answer 51

When legume pods dry, they split and seeds scatter in all directions. For example, pea pods.

Question 52

Describe and give an example of a plant with a water dispersal method

Answer 52

Seeds air cavities make them buoyant and able to float away. For example, a coconut palm.

Question 53

Describe and give an example of a plant with a carrying dispersal method

Answer 53

Hooked seeds attach to animal coats and are carried away. For example, burdocks.

Question 54

What are the different methods of seed dispersal?

Answer 54

Wind Transport Rolling Bursting Water Carrying

Question 55

What is the evolutionary advantage for a seed being able to go dormant?

Answer 55

Dormant seeds have a low metabolic rate, and so they survive very cold weather. The water content of a dormant seed is reduced below 10% and so seeds survive dry conditions.

Question 56

What is the evolutionary advantage for methods of seed dispersal?

Answer 56

Seeds can be dispersed so they do not compete with the parent plant, and it allows the colonisation of new habitats.

Question 57

How is the testa adapted?

Answer 57

It is chemically resistant so seeds survive adverse chemical conditions and it physically protects the embryo.

Question 58

Why are inhibitors an evolutionary advantage for plants?

Answer 58

As they only allow germination at a suitable time of year. They are broken down in very cold weather in vernalisation so that the seed can germinate in the spring.

Question 59

What is germination?

Answer 59

The process in which the plant grows from a seed. It begins with a very vigorous biochemical reaction and developmental activity and lasts until the first photosynthesising leaves are produced.

Question 60

What are the requirements for successful germination?

Answer 60

A suitable temperature- the optimum temperature is the optimum for the enzymes involved, usually 5-30C Water- to mobilise enzymes, for transport in the xylem and phloem and to vacuolate cells, making them turgid. Oxygen- aerobic respiration releases energy, which fuels metabolism and growth.

Question 61

Describe the process of germination

Answer 61

When conditions are suitable, water is imbibed by the micropyle. Water causes the tissues to swell and provides suitable conditions for enzyme activity. Food reserves are broken down into soluble molecules, with the soluble products being transported to the embryo and carried in the phloem to the apical meristems. The swollen tissues rupture the testa and the radicle emerges from the seed. It is positively geotrophic and negatively phototrophic so grows downwards. Then the plumule emerges which is negatively geotrophic and positively phototrophic so grows upwards. When the plumule emerges from the soil, it straightens out and the leaves begin to unfurl and photosynthesise.

Question 62

What macromolecules are involved in germination and how are they used?

Answer 62

Starch, hydrolysed by amylase into maltose is converted to cellulose for cell wall synthesis and for energy release. Proteins, hydrolysed by protease into amino acids are used to synthesise new proteins and for energy release.

Question 63

Why does the plumule emerge as a hook shape?

Answer 63

To prevent damage by soil abrasion.

Question 64

What are the apical meristems?

Answer 64

Places where rapid cell division occurs.

Question 65

When is germination complete?

Answer 65

As soon as the food reserves in the cotyledons have been depleted.

Question 66

Describe the synthesis of sugars from gibberellic acid in the barley seed

Answer 66

1. The seed secretes gibberellic acid which diffuses through the endosperm to the aluerone layer. 2. The gibberellic acid switches on genes in the cells of the aleurone layer, resulting in transcription and translation, producing enzymes such as proteases and amylases. 3. The proteases hydrolyse proteins in the aleurone layer to amino acids, which are used to make amylase and maltase. 4. The carbohydrates diffuse out of the aleurone layer and hydrolyse the starch stored in endosperm cells. 5. The sugars produced diffuse back through the endosperm to the plumule and radicle of the embryo. 6. Sugars are respired for energy, which fuels biosynthesis and cell division bringing the seed out of dormancy.