Chapter 25 - Sexual Reproduction In Plants Flashcards
Define unisexual flowers
Have stamen ( male) and carpel (female) on separate plants
Define bisexual flowers
Has stamens and carpels on same flower
Receptacle’s function
Bears the parts of the flower
Flower stalk’s function
Connects the flower to the stem
Sepal’s function
Protects flower while in developing bud stage
Carpel’s function
The female reproductive organs
Ovary’s function
Contains ovules and becomes the fruit
Ovule’s function
Contains female gametes and becomes the seed
Female gamete’s function
Fuse with male gamete to form diploid zygote
Style’s function
Carries the stigma and pollen tube grows through style
Stigma’s function
Pollen becomes attached during pollination
Stamen’s function
The male’s reproductive organs
Anther’s funtion
Contains pollen sacs which produce pollen
Filament’s function
Carries the anther to be exposed
Pollen sac’s function
Chambers of the anther in which pollen grains are formed
Male gamete’s function
Fuses with female gamete to form diploid zygote
Petal’s function
Attracts insects for pollination
Nectary’s function
Produces nectar
Nectar’s function
Sweet sugary solution insects feed on which causes pollination
Define pollination
Process in which pollen is transferred from anther to stigma of same species
Self pollination
Transfer of pollen from anther to stigma within the same flower
Cross pollination
Transfer of pollen from anther to stigma on another plant
Name 2 disadvantages of self pollination
- Reduces genetic variation
2. Reduces resistance to disease
Name 2 advantages of self pollination
- In harsh enviroments pollination can still occur
2. If plant has good characteristic it can be passed on
Advantages of cross pollination
- Causes more genetic variation
- Great ability to adapt
- More chance for survival
- Plants are more resistant to disease
Disadvantages of cross pollination
A lot of pollen is wasted
Main agents of pollination
- Wind
2. Insects
Other agents
- Water
- Animals
- Humans
Insect pollinated flowers
- Petals are large bright
- Have nectaries
- Flowers are scented
- Reproductive organs are enclosed
- Smaller anthers
- Smaller stigmas
- Pollen grains are sticky and spiky
Wind pollinated flowers
- Petals are small and dull
- Nectaries are absent
- Flowers not scented
- Reproductive organs are projected outside
- Large anthers
- Large feathery stigmas
- Pollen are smooth and light
Growth of pollen tube and double fertilisation
- pollen lands on stigma
- pollen absorbs fluid and produces tube
- growth is controlled by pollen tube nuclues
- the tube grows through stigma style and ovary
- two generative nuclei then move down the tube
- the tube grows towards the micropyle and ovule
- the tube raptures and the two male gametes enter the ovule
- one gamete fuses with egg and form zygote
- the other fuses with the two polar nuclei and form endosperm
- the endosperm is where nutrients are stored
- after fertilisation the petals, stamen and style dries out and fall off
Formtion of the fruit
- fruit is ripened ovary
* depends on method of dispersal
Formation of seed
- Develops from the ovule
- Zygote grows by mitosis to produce embryo
- Embryo consist of radical and plumule
- The triploid endosperm nucleus divides to form endosperm to store nutrients
- As seed matures the outer most layer becomes the testa
- The ovule becomes the seed and the ivary the fruit
Structure of non-endospermic seed
- seed is covered by testa
- the micropyle is a small hole in testa through which water and oxygen enters
- the hilum is a scar where the seed was attached to fruit
- the embryo is found between cotyledons
- embryo consist of radical and plumule
Define seed dispersal
The spreading out of seed and fruits as far as possible from mother plant
Importance of seed dispersal
- Avoids overcrowding
- Reduces competition
- Spreads to new environments
- Reduces risk of soil depletion
- Reduces risk of spreading disease
- Reduces natural disaster
Wind dispersal
- Surface area of seed increased
- Seeds increase buoyancy
- Are light and small
- Some seed has hair to float
- Some have wings
Animal dispersal
- Transport by sticking to fur of animal
- Hooked seed travel long distnces
- Succulent seeds can pass through digestive system
Water dispersal
May contain spongy tissue which allows it to float
Self dispersal
- Have mechanisms which throws seeds
- Depends on tension caused by drying out
- Suddenly splits open and seeds scatter
- Some plants explodes and seeds scatter
Seed germination
- Germination is the onset of growth of the embryo
2. Germination needs oxygen, water and suitable temperature to begin
Stages in germination
- Seed takes up water through micropyle
- Cotyledons swell and testa burst
- Enzymes become active
- Enzymes digest insoluble nutrients
- Digested nutrients used for growth and respiration
- Radical emerges from micropyle
- Testa falls off
- Plumule emerges out of soil
- Plumule grows into the shoot
- Shoots start carry out photosynthesis
State the funtion of flowers
They are the sexual organs of a plant
