Sexual Reproduction in Flowering Plants Flashcards
Draw the structure of a flower.
.
What is the function of the sepal?
To protect the flower (and to prevent it from drying out)
What is the function of the petal?
To attract insects to the flower for pollination
What is the function of the stamen?
To produce the pollen grains in the anthers. (Each pollen grain produces two male gametes, one of which can fertilise an egg cell)
What is the function of the anther?
Produces pollen
What is the function of the filament?
Holds the anther in place
What is the function of the carpel?
To produce the ovules (Each ovule contains an egg cell inside an embryo sac)
What is pollination?
Transfer of pollen from the anther to the stigma of a flower of the same species
What is the function of the stigma?
Where pollen lands after pollination
What is the function of the style?
Pollen travels down this
What is the function of the ovary?
Contains ovules
What is self pollination?
Transfer of pollen from an anther to a stigma of the same plant
What is cross-pollination?
Transfer of pollen from the anther to the stigma of a different plant of the same species
What adaptations do flowers have for animal (insect) pollination?
Petals brightly coloured, scented with nectaries.
Small amounts of sticky pollen.
Anthers inside petals.
Stigmas sticky, inside petals.
What adaptations do flowers have for animal (insect) pollination?
Petals small, not coloured brightly.
Anthers outside petals.
Stigmas large, feathery and outside petals.
Pollen Large numbers, light, dry and small.
What is fertilisation in plants?
Fertilisation is the fusion of the male (n) and female (n) gametes to produce a zygote (2n).
What type of gamete does the pollen grain produce?
The male gamete
What type of gamete does the embryo sac in a plant produce?
An egg cell and polar nuclei
How do seeds form after a zygote is formed?
The zygote grows repeatedly by mitosis to form an embryo.
What does and embryo consist of?
An embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for germination)
What happens to the endosperm nucleus and what does it then act as? What is an example of one?
The endosperm nucleus (3N) divides repeatedly to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed e.g. maize
What happens to the endosperm in non endospermic seeds? Where is food stored in these seeds and what is an example of one?
In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons e.g. bean
What is an endosperm?
A food store for developing embryo
What is in all seeds?
An embryo with a plumule (immature shoot), radicle (immature root) and cotyledon (food supply or seed leaf)
What is in some seeds?
An endosperm which is a food store
What are the two features that seeds are classified according to?
Number cotyledons (Seed leaves) Presence of endosperm
What are the two types of seeds as classified according to number of cotyledons (seed leaves)? Give examples.
Monocotyledon - one cotyledon e.g. maize.
Dicotyledon - two cotyledons e.g. broad bean
What are the two types of seeds as classified according to presence of endosperm? Give examples.
Present - endospermic e.g. maize
Absent - non-endospermic e.g. broad bean
What are differences between monocots and dicots?
Monocots have 1 cotyledon, parallel venation, scattered vascular bundle arrangement and petals usually in multiples of 3.
Dicots have 2 cotyledons, reticulate (net) venation, vascular bundle arrangement in a ring and petals usually in multiples of 4 or 5.
What are the features of a monocot?
Monocots have 1 cotyledon, parallel venation, scattered vascular bundle arrangement and petals usually in multiples of 3.
What are the features of a dicot?
Dicots have 2 cotyledons, reticulate (net) venation, vascular bundle arrangement in a ring and petals usually in multiples of 4 or 5.
How many cotyledons do monocots and dicots have?
Monocots have 1 cotyledon, dicots have 2 cotyledons
What venation do monocots and dicots have?
Monocots have parallel venation and dicots have reticulate (net) venation
What vascular bundle arrangements do monocots and dicots have?
Monocots have scattered vascular bundle arrangement and dicots have vascular bundle arrangement in a ring.
What number of petals do monocots and dicots have?
Monocots have petals usually in multiples of 3 and dicots have petals usually in multiples of 4 or 5.
In fruit what does the ovule become?
the seed
In fruit what does the ovary become?
the fruit
What is a fruit?
A fruit is a mature ovary that may contain seeds
What is the process of fruit formation stimulated by?
growth regulators produced by the seeds
What are the methods of the dispersal of seeds?
Wind, water, animals, self
What are examples of how wind disperses seeds?
Sycamore and ash produce fruit with wings.
Dandelions and thistles produce fruit with parachute devices.
Both help to disperse the seeds more widely using wind.
What are examples of how water disperses seeds?
Light, air filled fruits that float away on water e.g. coconuts, water lilies.
What are examples of how animals disperse seeds?
Sticky fruit - fruits with hooks that can cling to the hair of an animal and be carried away e.g. burdock, goose grass.
What are examples of how self disperses seeds?
Some fruits explode open when they dry out and flick the seed away e.g. peas and beans
What is dormancy?
A resting period when seeds undergo no growth and have reduced cell activity or metabolism.
What are the advantages of dormancy?
Plant avoids harsh winter conditions.
Gives the embryo time to develop.
Provides time for dispersal
What are the applications of dormancy in agriculture and horticulture?
Some seeds need a period of cold before they germinate.
It may be necessary to break dormancy in some seeds before they are planted for agricultural or horticultural purposes.
This can be done by placing them in the fridge before they are planted.
What is germination?
The re-growth of the embryo after a period of dormancy if the environmental conditions are suitable
Why is water necessary for germination?
- Activates the enzymes
- Medium for germination reactions e.g. digestion
- Transport medium for digested products
What are the factors necessary for germination?
A suitable temp. (Warmth), Oxygen and Water (WOW!)
Why is oxygen needed for germination?
Needed for aerobic respiration
Why is a suitable temperature necessary for germination?
Allows maximum enzyme activity
How does digestion take place in germination?
Digestion of stored food in endosperm and cotyledon
How does respiration take place in germination?
To produce ATP to drive cell division
When do events in germination cease?
Events in germination cease when the plants leaves have developed and the plant has started to photosynthesise.
What are the events in germination?
- Water is absorbed
- Food reserves are digested
- Digested food is moved to the embryo
- New cells are produced using amino acids
- Glucose is turned into ATP to drive cell division
- Radicle breaks through the testa
- Plumule emerges above ground
- New leaves begin to photosynthesise
What happens in asexual reproduction?
Part of the plant becomes separated from the parent plant and divides by mitosis to grow into a new plant.
What happens as a result of asexual reproduction?
As a result the offspring are genetically identical to the parent
What are runners?
Runners are horizontal running of the soil surface. Terminal bud of the runner sends up new shoots.
e.g. strawberry, creeping buttercup.
What are an example of modified stems?
Runners
What are an example of modified roots?
Root tubers
What are root tubers?
Root tubers are swollen fibrous roots. The tuber stores food, but the new plant develops from a side bud at the base of the old stem. e.g. dahlia, lesser celandine.
What are an example of modified leaves?
plantlets
What are plantlets?
Some plants produce plantlets along the edges of the leaves. Plantlets reach a certain size, fall off and grow into new plants. e.g. Lily, kalanchoe (mother of thousands)
What are an example of modified buds?
Bulbs
What is a bulb?
A bulb contains an underground stem, reduced in size. Leaves are swollen with stored food. e.g. onion, daffodil, tulip.
What are the advantages of sexual reproduction compared to asexual reproduction? (differences between them)
Sexual (seed) reproduction
Cross pollination ensures variation (allows evolution)
More resistant to disease
Dispersal reduces competition
Seeds can remain dormant and survive unfavourable conditions.
Asexual (vegetative) reproduction
No variations - can be advantage in commercial horticulture.
All plants are of same species susceptible to disease.
Overcrowding and competition.
No seeds formed - no dormancy.
What are the advantages of sexual (seed) vegetative propagation compared to asexual (vegetative) vegetative propagation? (differences between them)
Sexual (seed) Complex process Depends on outside agents for seed dispersal Slow growth of young plants to maturity Wasteful e.g. petals, pollen, fruit
Asexual (vegetative) Simple process No outside agents needed Rapid growth No waste
What are methods of vegetative propagation?
Cuttings, Grafting, Layering, Micropropagation (Tissue Culture), Cloning
What does an anther consist of?
four chambers called pollen sacs
What is each pollen sac protected by?
a fibrous layer
What is inside the fibrous layer of a pollen sac?
Inside the fibrous layer is the tapetum - a food store that supplies energy for cell divisions in the pollen sac.
Draw the anther and the pollen sac.
.
How do pollen grains develop?
Microspore mother cells (2n) are located in the pollen sacs. They are diploid. They divide by meiosis to produce a group of four haploid cells called a tetrad. Each tetrad breaks up to form four separate haploid pollen grains.
What happens to a haploid pollen grain as it develops?
Pollen grains divide by mitosis producing two haploid nuclei. Tube nucleus - forms the pollen tube. The generative nucleus forms the male gametes.
What happens after pollination?
The generative nucleus (n) divides by mitosis to form two sperm nuclei (n). These will each play a role in double fertilisation.
What is in the embryo sac?
Each ovary contains one or more ovules. An ovary has two walls called integuments. Between the integuments is a small opening (micropyle) through which a pollen tube can enter. The nucellus provides nutrients for growth in the ovule.
How is the embryo sac prepared?
One cell in the ovule the megaspore mother cell (2n) divides by meiosis to form four haploid cells. Three of these cells disintegrate. The remaining cell is called the embryosac.
How does the nucleus of the embryo sac prepare?
The nucleus of the embryo sac (n) divides by mitosis three times forming eight haploid nuclei. These are still contained within the embryo sac. Five of these nuclei will later disintegrate. The remaining three are the gametes. Two of these form the polar nuclei in the embryo sac. The remaining female gamete forms an egg cell.
