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IGCSE Biology study notes-2022-syllabus

TOPICS FOR  0620- IGCSE BIOLOGY EXAMINATION [ VALID  FOR EXAMS UPTO 2022 ]

1. Characteristics and classification of living organisms

2. Organisation of the organism

3. Movement in and out of cells

4. Biological molecules

5. Enzymes

6. Plant nutrition

7. Human nutrition

8. Transport  in plants

9. Transport in animals

10. Diseases and immunity

11. Gas exchange in humans

12. Respiration

13. Excretion in humans

14. Coordination and response

15. Drugs

16. Reproduction

17.Inheritance

18.Variation and selection

19.Organisms and their environment

20.Biotechnology and genetic engineering

21.Human influences on ecosystems

TOPIC:16-REPRODUCTION:

ASEXUAL REPRODUCTION

Asexual reproduction is a process resulting in the production of genetically identical offspring from one parent

Examples of asexual reproduction:

EXAMPLE: 1

The diagram shows a plant reproducing asexually by growing a plantlet from the parent plant. The plantlet produced is identical. Any changes can be attributed to gene modification.

Asexual reproduction-Runners-Plantlets

EXAMPLE:2

Examples of unicellular organisms that undergo binary fission are amoeba, paramecium, Leishmania etc.

Asexual reproduction-Binary fission

EXAMPLE:3

SPORE FORMATION BY THE FUNGUS:

The parent plant produces hundreds of reproductive units called spores in its spore case. When this spore case of the plant bursts, the spores are released and they travel in air and land on food or soil. Here they germinate and produce new plants.

Asexual reproduction -Fungus

ADVANTAGES OF ASEXUAL REPRODUCTION to a species in the wild and crop production:

  • Favourable characteristics of parents are passed on.
  • Dense colonies outcompete other species.
  • Less energy/resources are used.
  • Only one parent is needed.
  • If parent is well adapted then the offspring will be well adapted to the environment

DISADVANTAGES OF ASEXUAL REPRODUCTION to a species in the wild and crop production:

  • There is competition for resources.
  • There is little or no variation
  • Less evolution[or] Less ability to adapt to the change.
  • It is possible that all may get killed by a single disease.

 

16.2: SEXUAL REPRODUCTION :

Definition:

  • SEXUAL REPRODUCTION: It is a process involving the fusion of the two nuclei of two gametes (sex cells) to form a zygote and the production of offspring are genetically different from each other.
  • FERTILISATION: It is the fusion of gamete nuclei.

Note:

  • The nuclei of the gamete are haploid
  • The nuclei of the zygote are diploid.

 

ADVANTAGES OF SEXUAL REPRODUCTION TO AN ANIMAL SPECIES:

  • The population of the species can be increased.
  • It allows variation within the species which is caused by independent assortment.
  • Recessive traits can also get expressed.
  • The organism can adapt better to changing environment.
  • It allows the evolution of species.
  • There is seed dispersal
  • There is colonization

 

DISADVANTAGES OF SEXUAL REPRODUCTION TO AN ANIMAL SPECIES:

  • Needs two parents [or] Needs a pollinating agent.
  • Much pollen is wasted [ or many seeds are wasted]
  • Fertilisation may not happen
  • There is a loss of a lot of energy

 

16.3: SEXUAL REPRODUCTION IN PLANTS:

PARTS OF AN INSECT POLLINATED FLOWER:

Parts of a flower

FOLLOWING ARE THE FUNCTIONS OF THE:

  • Sepals: It protects the flower when in the bud  condition
  • Petals: In insect-pollinated flowers, its function is to attract insects .
  • Anthers: To produce sex cells
  • Stigmas It is the top of the female part of the flower and it’s function is to collects pollen grains
  • Ovaries: It’s function is to produce the female sex cells

 WIND POLLINATION:

wind pollination

INSECT POLLIANTION:

INSECT POLLINATION

COMPARING THE FEATURES OF INSECT POLLINATED AND WIND POLLINATED FLOWERS:

  • The flowers are dull green or brown or  not colourful
  • There are small petals [ or] There are lack of petals
  • Flowers are small or inconspicuous
  • Bracts are presence
  • Filaments are long
  • Anthers/Stigmas hang out of the flowers
  • Anthers are loosely attached
  • Stigmas hang out of the flowers
  • Stigmas are feathery
  • Stigmas  have a large surface area
  • Larger amount of pollen are produced.
  • There is no nectary
  • Flowers do not have scent

FEATURES OF POLLENS OF WIND POLLINATED FLOWERS:

 

  • Pollen is light
  • Pollen is nit sticky/is smooth
  • Pollen has a large surface area
  • Large amounts of pollen are produced
  • Pollen is small

 SELF AND CROSS POLLINATION:

Self pollination and cross pollination