IGCSE BIOLOGY Unit 3 thebiotutor

Igcse Biology Unit 3 Thebiotutor-Free PDF

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Biology Notes Unit 3 Reproduction Inheritance,A Reproduction. B Inheritance,A Reproduction,Students will be assessed on their ability to. 3 1 describe the differences between sexual and asexual reproduction. 3 2 understand that fertilisation involves the fusion of a male and female gamete to produce a. Asexual Reproduction, Reproduction in which there is only one parent and the offspring are clones have the. same genes unless mutations occur,Process by which cells asexually reproduce. Produces offspring called daughter cells who are genetically identical to the parent. unless a mutation occurs, Used to replace dead or damaged diploid cells in plants and animals.
Also used for normal growth of diploid cells, Diploid cells body cells with a full set of chromosomes 46 in humans. Does NOT occur in sex cells,Process of Mitosis,1 Chromosomes become coiled and visible. 2 Each chromosome makes an exact copy of itself, 3 Chromosomes and their copy line up down the equator of the cell. 4 Chromosomes are pulled apart and move to opposite ends of the cell. 5 Cell splits into two new daughter cells with the exact same chromosomes as the. Advantages of Asexual Reproduction,Only one parent required no mates needed. Quick way of producing a large number of cells, Daughter cells are genetically identical to parent cells so parent cells are easy to.
Simple and reliable process,Disadvantages of Asexual Reproduction. No genetic variation cells have a very hard time adapting to change. Sexual Reproduction,Definition, Reproduction in which an individual is formed by the combination of 2 sex cells from. two parents and offspring are not genetically identical. New organisms are created by the fusion of gametes sex cells from two parents. called fertilisation, Fertilisation creates a normal diploid cell called a zygote which then grows by. Offspring s genetic characteristics are created from a mixture of the 2 sets of. chromosomes so it will inherit features from both parents. Process by which gametes sex cells are made for sexual reproduction. Gametes are haploid they contain half the chromosomes of a normal body cell 23. o Male gametes Sperm cells,o Female gametes Egg cells. Gametes are formed in testes and ovaries from the meiosis of reproductive cells. o Male gametes Pollen cells,o Female gametes Ova or egg cells.
Gametes are formed in Anther and ovaries from the meiosis of reproductive cells. Process of Meiosis, 1 Chromosomes of the reproductive cell fatten and become visible. 2 Each chromosome makes an exact cop of itself,3 Chromosomes line up down the equator in pairs. 4 The chromosome pairs swap genes crossing over split up and move to opposite. ends of the cell,5 The cell spits into two new cells. 6 The chromosomes are pulled apart in each new cell and move to opposite ends of. 7 The two new cells spit again to make four new haploid cells genetically different. from the parent cell,Advantages of Sexual Reproduction. Genetic variation occurs in many stages,o Line up of pairs of chromosomes is random.
o Crossing over swapping of genes among pairs of chromosomes is random. o All gametes are genetically different from their parents and an organisms can. produce gametes with billions of different combinations of chromosomes. o The fusion of male and female gametes is random it could be any gamete. from the male and female,Species can adapt to changes in their environment. Disadvantages of Sexual Reproduction, Two parents required organisms need to find a mate. More complex process there is a higher chance of a mutation occurring. Fertilisation, The fusion of male and female gametes to produce a zygote. Occurs when a nucleus from a pollen grain fuses with the nucleus in the egg sac. Steps of fertilisation,1 Pollen grain lands on top of the stigma. 2 Pollen tube is formed by the tube nucleus one of the two nuclei in the grain cell. 3 Tube grows up to the micropyle in the egg sac a tiny hole in the egg sac. 4 Tube nucleus joins with another nucleus in the egg sac The new nucleus will. grow to form the endosperm a food supply for the growing zygote. 5 Second nucleus passes through the pollen tube to the egg cell and joins with the. egg cell nucleus This produces the zygote, 6 The plant starts to turn the carpel into a fruit and the ovule s become seed s.
Seeds protect the zygote until it is ready to germinate after the seed has been. distributed,Flowering plants,Students will be assessed on their ability to. 3 3 describe the structures of an insect pollinated and a wind pollinated flower and explain. how each is adapted for pollination, 3 4 understand that the growth of the pollen tube followed by fertilisation leads to seed and. fruit formation, 3 5 recall the conditions needed for seed germination. 3 6 understand how germinating seeds utilise food reserves until the seedling can carry. out photosynthesis, 3 7 understand that plants can reproduce asexually by natural methods illustrated by runners. and by artificial methods illustrated by cuttings,Asexual Reproduction in Plants.
Also called vegetative reproduction,Plants produced are genetically identical. Occurs naturally in some plants such as strawberries. Runner grows out from the base of the parent plant. Grows along the ground until the runner reaches a suitable patch of soil. The runner develops roots in the soil, When the root system has grown enough the stem connecting the offspring to the. parent withers and falls off,Does not occur naturally man made method. Cutting is a piece of a plant that has been cut off from it. The cutting is placed in the ground and a root hormone compound is added. The cutting then grows into a plant that is genetically identical to the plant from. which it came, Cuttings are useful for farmers who want to produce plants with the best genetics for. fruit vegetable grain production They can just take a cutting of the best plant and. grow the same plant again,Sexual Reproduction in Plants.
Occurs in flowering plants the most successful group of plants. Flowering plants reproducing sexually have these adaptations They can. o Produce both male and female gametes,o Transfer gametes between flowers. o Fuse the gametes to produce a zygote,o Produce seeds the embryo with food stores. o Distribute seeds,Floral Structure, All flowering plants have about the same arrangement of structures for sexual. reproduction,Male Parts,Entire male part Stamen,Consists of. o Anther at the top of a stem structure called the filament. All flowers have more than one stamen, Pollen grains containing the male gametes are developed in the anthers.
Cells in the pollen sacs of the anthers divide by meiosis to create cells for pollen. When all pollen grains are formed anther splits open to release them. Female Parts,Entire female part Carpel, Carpel produce the female gametes ova or egg cells. Consists of,o Stigma at the top collects pollen grains. o Style connects stigma to the ovary,o Ovary ovum contains ovule. o Ovule contains the one ova produced by meiosis surrounded by an egg sac. for protection, Carpel protects the ova from the external environment. Flowers contain one or more carpel,Pollination Fertilisation and Germination.
Pollination,Definition, Process of transferring pollen from stamen to carpel. Cross Pollination,The transfer of pollen from one plant to another. Two types of cross pollination,o Wind Pollination,o Insect Pollination. Plants that pollinate using the wind and plants that pollinate using insects have. different structures which enable the plant to pollinate effectively using the method. Wind Pollination, Plants pollinated by wind will have tall stamens with anthers exposed to wind. usually above the petals, They produce light pollen grains which are easily carried by the wind.
They also have feathery Stigmas to enable them to catch the light pollen grains from. Not usually brightly coloured nor do they produce nectar as they do not rely on. E g Grasses cereals trees etc,Insect Pollination, Plants pollinated by insects will have tall stamens with anthers above the petals. They produce sticky pollen grains which are easily carried by the insect. They also have sticky Stigmas to enable them to catch the light pollen grains from. the insect, Usually brightly coloured produce fragrant smells and nectar to attract the insects. Insects goal is to retrieve the sweet nectar which they use for energy While. retrieving the nectar the pollen sticks to them and is transferred from plant to plant. E g Most flowering plants honey suckle etc,Self Pollination. Occurs when the pollen of a plant is transferred to the stigma of the same plant. Most plant try to prevent self pollination, Some have flowers which are just one sex or the other. Some have flowers with male and female parts that mature at different times. Pollen from other plants are more likely to fertilise an egg in the ovule anyway. because pollen grains from the same plant tend to grow slower than foreign grains. Fertilisation Pollen tubes, Once the pollen tube lands on the stigma it starts to grow a pollen tube from the pollen.
This pollen tube will follow sugar solution down the inside of the style into the ovary. into the ovule and allows the transfer of the pollen nucleus to the nucleus of the ovum. As the pollen tube grows the nucleus of the pollen grain travels down it. Fertilisation occurs when the pollen nucleus fuses with the nucleus of the ovum. Ovary becomes Fruit,The Ovary swells and becomes the fruit. The Fertilised ovum becomes the seed, Many pollen can fertilise many ovules and so many seeds can be formed. Seed Structure, Endospermic seeds contain large stores of endosperm to supply the plant with. nutrients as it germinates, In non endospermic seeds the endosperm is used to make large storage organs called. cotyledons, The cotyledons are the first leaves of the plant even though they don t resemble.
Plants that have two cotyledons are called dicotyledonous plants. Plants that have one are called monocotyledonous plants. Radicle young root,Plumule first shoot of the embryo. Germination,Definition,Process by which a seed develops into a plant. 1 Seed absorbs a large amount of water to help enzymes work and to inflate cells. 2 Enzymes break down starch from the food reserves usually endosperm into smaller. sugars Sugar is used for respiration to produce energy for the plant s growth The. plant doesn t have leaves so it can t get its energy from photosynthesis yet. 3 Water potential drops as sugar is broken down so seed absorbs even more water. 4 Respiration rate rises, 5 Seed grows into embryo plant with a radicle and plumule which eventually develops. leaves At this point the plant starts photosynthesising and the plant is no longer. germinating, Light isn t needed for germinating seeds to grown because they use food reserves. instead of photosynthesis,Reproduction in flowering plants.
1 Which is the most accurate statement, The principal role of a flower in the life cycle of a plant is. a attracting insects,b producing seeds,c producing pollen. d producing nectar, 3 What is a the male gamete and b the female gamete in a flowering plant. 4 Complete the following paragraph selecting words from the list below Pollination. is the transfer of from the to the in a flower In cross pollination the. from a flower on one is transferred to the of another of the same. anthers ovule stigma plant flower pollen ovary petal style receptacle. 5 Complete the following sentences, In a flowering plant fertilisation occurs when the of the fuses with the. of the After fertilisation the becomes the and the becomes. 6 Which of the following statements is correct In flowering plants. a pollination can take place without fertilisation. b fertilisation can take place without pollination. c pollination and fertilisation are the same, d pollination and fertilisation must occur at the same time.
7 Some species of plant are strongly adapted to pollination by certain insects Which. of the following characteristics would you regard as adaptations to pollination by. a white or coloured petals f small green petals, b light smooth pollen grains g production of nectar. c spiky or sticky pollen grains h production of pollen. d anthers and stigma inside the flower i production of scent. IGCSE BIOLOGY Unit 3 Reproduction amp Inheritance Unit 3 Andy Todd Biology Notes Unit 3 Reproduction amp Inheritance Contents A Reproduction B Inheritance Unit 3 Andy Todd A Reproduction Students will be assessed on their ability to 3 1 describe the differences between sexual and asexual reproduction 3 2 understand that fertilisation involves the fusion of a male and female gamete to

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