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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- Click here to view the video flip book

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.

EXAMPLE:2

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

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.

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.

BOARD EXAM QUESTION:
Describe the process of reproduction in bacteria: 3 marks

Bacteria reproduce by binary fission by motosis. In this process the bacterium, which is a single cell, divides into two identical daughter cells. 
Binary fission begins when the DNA of the bacterium divides into two (replicates). .Each daughter cell is a clone of the parent cell.

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 
• There is a loss of a lot of energy

DISADVANTAGES OF SEXUAL REPRODUCTION TO  A PLANT 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:

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:

INSECT POLLIANTION:

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:

SEXUAL REPRODUCTION IN HUMANS:

1. Labeled diagram of the male reproductive system

 

2-PARTS AND FUNCTIONS OF THE MALE REPRODUCTIVE SYSTEM:

• PENIS-To insert semen into vagina
• URETHRA-To pass semen through penis
• TESTIS-To make sperm(testosterone)
• VAS DEFERENS(Sperm duct)-To pass sperm from testis to urethra
• SROTUM-To keep the testis at a temperature lower than that of  the body
• PROSTRATE GLAND-To produce seminal fluid
• EPIPIDYMUS-To mature an store the sperm

3. LABELLED DIAGRAM OF THE FEMALE REPRODUCTIVE SYSTEM

4.STRUCTURE AND FUNCTIONS OF THE FEMALE REPRODUCTIVE SYSTEM

• OVARIES-To produce the hormones oestrogen and progesterone/ It is also the site of egg development and ovulation
• FALLOPIAN TUBES-(Oviducts)-Carry the ovum from the ovary to the uterus
• UTERUS-Place for embryo and fetus developement
• CERVIX-Involved in menstruation/ It holds the fetus in place during pregnancy/ Dialates during birth to allow the fetus to leave the uterus.
• VAGINA-Provides a passageway for the sperm and menstrual flow/ It also functions as the birth canal

5 ROLE OF PLACENTA IN MAINTAINING PREGNANCY:

• It secretes progesterone to keep the lining of the uterus thick to maintain pregnancy in-order to prevent the breakdown of the uterus lininG

6. ROLE OF PLACENTA IN THE DEVELOPMENT OF THE FETUS: board question-4m

1.  Exchange of  materials e.g. oxygen/glucose/ water/amino acids/antibodies/urea/carbon dioxide;
2. Acts as a physical attachment between fetus and uterus/mother t
3. Prevents  the mixing of  mother and fetal blood
4. Protects against  mother’s (high) blood pressure
5.  Plays protective role in preventing the entry of some pathogens A
6. It  secrets  progesterone to keep lining of uterus thick/prevents menstruation/to prevent breakdown of uterus lining or it prevents uterine muscle contracting 

7 FUNCTIONS OF THE PLACENTA

• It acts as a barrier between the blood systems and thus prevents the mixing of the maternal and the fetal blood
• It supplies oxygen to the fetus
• It supports the fetus
• It protects against sudden movements and bumps
• It helps to lose carbondioxide and urea from the fetus
• It helps to transfer antibodies from the mother
• It helps to supply and remove water

8. EXCHANGE OF MATERIALS ACCROSS THE PLACENTA

THE FOLLOWING SUBSTANCES PASS FROM THE MOTHER TO THE FETUS:

• Oxygen
• Glucose
• Amino acids
• Lipids/fattu acids and glycerol
• Vitamins
• Ions ( Na, Ca, Fe_
• Alcohol, nicotine and other drugs
• Viruses
• Antibodies

THE FOLLOWING SUBSTANCES PASS FROM THE FETUS TO THE MOTHER:

• Carbondioxide
•  Urea and other waste products

8. FUNCTIONS OF AMNIOTIC FLUID AND AMINIOTIC SAC:  BOARD QUESTION-[2 MARKS]

AMNIOTIC FLUID::

1. Protects fetus from physical damage/cushions; 
2. It acts as shock absorber AW ; REJECTED ANSWER:prevents shock /PROVIDES SUPPORT
3.  Prevents unequal pressures from acting on fetus/
4. maintains constant environment/allows free movement
5. Protects fetus from temperature fluctuations  REJECTED insulates
6.  Protects fetus from drying out  

AMNIOTIC SAC:

1. Scretes/produces amniotic fluid
2. Encloses/contains THE  amniotic fluid 

COMPLETE SET OF THE ABOVE pdfs at our membership website: Link

9.CHILD-BIRTH

 

 

10.BIRTH CONTROL METHODS-Board-Question-12MARKS

• Natural:

1. It the rhythm method or the calendar method.It is important to know the pattern of the mentstrual cycle. There should be no intercourse when egg is in the oviduct.One indicator of ovulation is the rise in the body temperature
2. The next natural method is to withdraw the penis from the vagina  before ejaculation to prevent sperm comming in contact with the egg
3. The last natural method is abstinence from sex to avoid pregnancy

• Chemical:

1. Contraceptive pills that contain progesterone and oestrogen prevent ovulation
2. Morning-after-pill: this pill prevents the fertilised egg from implanting in the uterus
3. Spermicidal cream applied to vagina kills the sperms

• Mechanical:

1. Using a condom prevents sperm comming in contact with the eggs
2. Use of IUD prevents the fertilised eggs from implanting in the uterus

• Surgical:

Vasectomy/Laparotamy: In vasectomy oviducts are cut and sealed and in laparotamy the sperm ducts are cut so that no eggs an dsperm can pass through

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