REPRODUCTION IN PLANTS
PPT
REPRODUCTION :
- Reproduction is one of the fundamental characteristics of all living organisms.
- Reproduction is defined as a biological process that make more of the same kind of organisms- new individuals.
- Reproduction enables the continuity of the species, generation after generation
- Each kind of organism has its own particular method of reproducing, but all of these methods fit into one of two categories.
TYPES OF REPRODUCTION
1_ASEXUAL REPRODUCTION
Features:
- It involves one parent only.
- The offspring are genetically identical to their parent
- No specialized cells like gametes are produced.
- Large number of organisms produced in a very short time.
Examples of asexual reproduction:
2. Spore production in fungi
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3. Tuber formation in potatoes
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ADVANTAGES AND DISADVANTAGES OF ASEXUAL REPRODUCTION:
ADVANTAGES OF ASEXUAL REPRODUCTION
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DISADVANTAGES OF ASEXUAL REPRODUCTION
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2_SEXUAL REPRODUCTION
Features:
Sexual reproduction is a process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.
- It involves two parents.
- Specialized sex cells gametes are produced.
- In animals male gametes are sperm cell and female gametes are egg cells.
- In flowering plants the male gametes are inside the pollen grains and female gametes are inside the ovules. (discussed later)
- During sexual reproduction the gametes fuse together at fertilisation and form zygote.
- Zygote divides to form an embryo which may grow into a new individual plant.
- The offspring shows genetic variations.
- Comparatively less number of organisms produced.
Sexual reproduction is a process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.
ADVANTAGES AND DISADVANTAGES OF SEXUAL REPRODUCTION:
ADVANTAGES OF SEXUAL REPRODUCTION
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DISADVANTAGES OF SEXUAL REPRODUCTION
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SEXUAL REPRODUCTION IN PLANTS :
FLOWER STRUCTURE
- Flowering plants carry out sexual reproduction by producing flowers.
- Flowers vary in structure depending upon their method of pollination.
- INSECT POLLINATED FLOWERS
- WIND POLLINATED FLOWERS
INSECT POLLINATED FLOWERS :
PARTS OF FLOWER AND THEIR FUNCTION: Flower parts are often arranged in rings attached to the end of a swollen flower stalk.
- Sepals: Sepals are leaf like structures that protect the flower when it is a bud.
- Petals :Petals are often large,brightly coloured and scented.
- Nectary : Petals may have nectary at the base, which makes sugary nectar.
- Stamen :The male reproductive part of the flower, made up of anther and stamen.
- Anther : Contains pollen sacs, in which pollen grains are formed. Pollen contains male gametes.
- Filament: It is the stalk which hold and support the anther.
- Carpels : The female reproductive part of the flower, made up of stigma, style and ovary.
- Stigma: A stick surface that receives pollen during pollination.
- Style : Links the stigma to the ovary, through which pollen tubes grow.
- Ovary : Contains ovules, which develop into seeds when fertilised.
- Ovules: The ovules are inside the ovary. Each ovule has a female gamete (egg cell)
WIND POLLINATED FLOWERS
PARTS OF FLOWER AND THEIR FUNCTION :
- Grasses and cereals are all pollinated by the wind.
- These types of flowers are small, green and inconspicuous compared with insect-pollinated flowers.
- They have no scent and no nectar.
- Sepals and petals are very small in size.
- The anthers hang outside the flower so the wind can blow away the large quantities of small, smooth and light pollens that they produce.
- Pollen grains : larger amount of pollen grains are produced.
- The stigma is feathery and positioned outside the flower.Provide large surface area for catching pollen grains.
POLLINATION
- DEFINITION: Pollination is the transfer of pollen grains from the anther to a stigma of a plant of the same species.
- AGENTS OF POLLINATION :
- Pollination may be carried out by insects or by the wind.
- The structural adaptations of a flower depend on the the agent of pollination.
- COMPARE THE DIFFERENT STRUCTURAL ADAPTATIONS OF INSECT-POLLINATED & WIND POLLINATED FLOWERS
- TYPES OF POLLINATION.
- Types of pollination: The basic modes of pollination are
- Self pollination
- Cross pollination
- Self pollination: Transfer of pollen grains from the anther to stigma of the same flower or another flower on the same plant is said to be self pollination.
- Cross pollination : Transfer of pollen grains from the anther of a flower from one plant to the stigma of the flower on another plant of same species is called cross pollination.
IMPLICATIONS TO A SPECIES OF SELF-POLLINATION AND CROSS POLLINATION
- Cross pollination is of greater benefit to a species of plant, since it ensure exchange of genetic material between different plants and results in greater variations.
- Self pollination results in much less variation, since genetic material is not exchanged with different plant but with the same one. However self-pollination is an advantage if there are no pollinating insects and plant growing in isolation from others of the same species. Less chance of adapting to changing conditions. Less wastage of pollen.
FERTILISATION
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FORMATION OF SEED AND FRUIT
- After fertilisation, each ovule grows to form a seed.
- Each seed is made up of :
- Embryo : the zygote divides by mitosis and grow into embryo. The embryo consists of radicle and plumule.
- A food store : Food stores called cotyledons.
- A seed coat (testa) : The wall of the ovules forms the seed coat
- The ovary wall develop into a fruit, which may be fleshy (e.g. plum) or a dry pod (e.g. pea).
SEED STRUCTURE
Looking at seed structure:
- Seed coat (testa) : The seed coat is a tough, protective layer which prevents the embryo from being damaged and stops the entry of bacteria and fungi.
- Embryo: After fertilisation the zygote grows into an embryo. The embryo develops two cotyledons (seed leaves), a plumule and a radilce.
- - Radicle: will grow into the root during germination.
- -Plumule: will grow into shoot during germination.
- -Cotyledons: stores food require during germination.
- Micropyle : The micropyle is a small hole in the testa which allows water to enter so that the enzymes can be activated.
FRUIT STRUCTURE
- While the seeds are forming, the ovary swells into a fruit to protect the seed.
- The wall of the fruit is called the pericarp (which means around the carpel).
- In some fruits pericarp is fleshy .(Papaya, tomatoes etc.)
- Others have dry and may be quite hard. (Poppies, Oak, Cocklebur)
- After fertilization, many of the flower parts are not needed any more, so the sepals, petals and stamen wither and fall off.
- The structure of the fruit is related to the way in which its seeds are dispersed.
DISPERSAL OF FRUITS AND SEEDS
- WHAT IS SEEDS DISPERSAL..?
- The function of fruit is to spread the seeds.
- Seed dispersal is the scattering of the seeds all over the place to colonize the area away from the parent plant. It helps to reduce overcrowding at one place.
- WHY DO SEEDS NEED TO BE DISPERSED...?
- Dispersal helps plants colonise new area and avoids them all growing together and competing for following resources.
- Space,
- Light,
- Nutrients
- Water
- AGENT OF DISPERSAL : Seeds can be dispersed by following agents.
- Dispersal by wind
- Dispersal by animals
- Dispersal by water
- Dispersal by their own (mechanical)
A) DISPERSAL BY WIND
- Features of fruits and seeds dispersed by the wind are as following:
- Light weight seeds.
- May have a parachute
- May have wings.
- Examples: Dandelion, Sycamore
B) DISPERSAL BY ANIMALS
- There are two main modifications of fruits for animal dispersal.
- Succulent fruit (Fleshy and bright coloured fruits)
- Hooked fruits
VIDEO LINK : SEED DISPDERSAL
GROWTH AND DEVELOPMENT
GERMINATION OF SEEDS
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- Seed germination :
- Germination is a process when the seed develops into a seedling.
- The process of germination starts with the seed absorbing water.
- The absorption of water activates enzymes that increases respiration.
- The plant cell divide rapidly and the embryo inside the seed becomes large, and the radical (first root)of the plant emerges from the seed coat.
- After the radicle has appeared, the plumule starts to grow upwards towards light.
- When it reaches the light its growth slows and the first leaves spread out to absorb light and photosynthesis.
- The seedling continue to use the stored food until its own leaves are able to make enough food by photosynthesis for all its needs.
CONDITIONS FOR GERMINATION
- 1.WATER
- Water is needed for seed to swell. This swelling breaks the testas of some seeds.
- Activate enzymes.
- Transport of simple materials to the embryo.
- 2.OXYGEN
- Oxygen is needed for aerobic respiration to provide the embryo with energy.
- 3.WARM TEMPERATURE
- Suitable warm temperature is needed for efficient enzyme action