Biology IGCSE - Reproduction

Reproduction

production of new members of species, replacing those who died

Asexual reproduction

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

Asexual production involves

1 parent → NO gametes

Asexual reproduction pros and cons

Cons	Pros
Little variation in offspring → genetically identical → less resistant to changes → e.g. disease could wipe out all members of genetically identical species	Fast → can produce large number of offspring quickly

Gene

A length of DNA that codes for protein

Chromosome

thread - like structure of DNA → carry genetic information in form of genes

Diploid

Having 2 complete sets of chromosomes → humans have 23 sets

Haploid nucleus

having only 1 set of chromosomes

Gamete

a sex cell with half the normal number of chromosomes → HAPLOID

Fertilisation

fusion of 2 nuclei of 2 gametes

Zygote

cell formed by the fusion of 2 gametes → DIPLOID

Sexual reproduction

fusion of nuclei of 2 gametes to form a zygote → production of offspring are genetically different

Species

group of organisms that can reproduce to produce fertile offspring

Sexual reproduction pros and cons

Cons	Pros
Slower → requires 2 parents → takes longer	Variation in offspring → species better able to survive changes → e.g. a disease → also allows for evolution over time

Insect pollinated plant

Sepal

leaf - like structure → forms ring outside the petals

Petals

Coloured structure → attracts insects or birds to flower

Stamens

Male parts of flower

Anther

structure at the top of a stamen → inside which pollen grains are made

Stigma

part of the flower that receives pollen

Ovary

part of the flower that hold ovules

Ovules

Structure that contains female gametes

Carpels

Female reproductive parts of the plant → has stigma, style + ovary

Styles

Tube - like structure between stigma + ovary → pollen tube grows through it

Pollination

transfer of pollen grains from male part (anther of stamen) to the female part (stigma)

Fertilisation in plants

pollen nucleus (male gamete) fuses with a nucleus in the ovule (female gamete) → happens inside the ovary

Wind pollinated plants

Structural adaptations

Structure	Insect pollinate	Wind pollinated
Petals	Large colourful petals → attract insects	No/few small petals
Nectary	Nectaries in the base of petals → produces nectar → attracts animals	No nectaries
Scent	Strong scent → attractive to animals	No scent
Stigma	Inside the plant → insects brush past stigma to get nectar	Large + feathery → rough/sticky surface → traps pollen easily
Stamen	Inside flower → insects brush past anther to get nectar → produces sticky pollen	Dangles outside → easily accessible to wind → produces lots of smooth, light pollen

Need for water in germination

Water is absorbed by the seed → activates enzymes → enzymes break down food stores → provides energy for growth

Need for oxygen in germination

Oxygen is required for aerobic respiration → releases energy from food stores → energy used for cell division + growth

Need for suitable temperature in germination

Enzymes controlling growth work best at optimum temperature → too cold = slow activity → too hot = enzymes denature → no germination

Wind pollinated plants

Anther	Stigma
Outside flower Hangs loosely → sways easily Produces large amount of light + smooth pollen	Large + feathery Hangs outside Large surface to catch pollen

Male reproductive system

Female reproductive system

Testosterone

Produced by testes → stimulates sperm production

Testosterone secondary sexual characterises

• Growth of facial + body hair

• Deeper voice

• Increase muscle mass

• Growth of penis + testes

Oestrogen

Produced by ovaries → regulates menstrual cycle

Oestrogen secondary sexual characteristics

• Development of breast

• Widening hips

• Start of menstrual cycle

• Growth of uterus + vagina

Menstrual cycle → Day 1 - 7

• Menstruation

• Endometrium breaks down → passes out of vagina → triggered by sudden progesterone drop

Menstrual cycle → Day 8 - 14

• Egg cell starts to mature Menstrual cycle → endometrium grows + thickens again → in case fertilise egg needs to implant itself

Menstrual cycle → Day 14

• Ovulation → egg goes through fallopian tube → released from the ovary

• Meet sperm → fertilises in fallopian tube OR no sperm → continues along fallopian tube

Menstrual cycle → Day 15 - 28

• Continues until day 1 → restarts again

Adaptive features of sperm → flagellum

• Tail like structure

• Helps swim towards egg → enables movement along female reproductive tract

Adaptive features of sperm → mitochondria

• Releases energy during respiration

• Power flagellum for long distances

Adaptive features of sperm → acrosome enzymes

• Found in head of sperm

• Contains enzymes to break down egg’s membrane

• Allows sperm to penetrate egg for fertilisation

Adaptive features of egg → energy stores

• Contains cytoplasm with energy rich nutrients

• Provides energy for early cell divison

Adaptive features of egg → jelly coat

• Surronds egg

• After fertilisation → hardens to prevent other sperm from entering

Female VS Male gamete

Feature	Egg	Sperm
Size	Large	Small
Motility	Non - motile	Motile → flagellum
Numbers	One egg released per menstrual cycle	Millions produced daily

STIs

Disease caused by pathogens that are transmitted during sexual contact

HIV

Virus which destroys white blood cells → reduces ability of immune system to defend other pathogens

HIV pathogen

is a pathogen caused by an STI

HIV infections may lead to AIDS

How HIV is transmitted

• Sexual activity → e.g. semen + blood

• Blood contact → sharing needles (drug use) → blood transfusions

• Mother to baby → during pregnancy, birth + breast feeding

How the spread of STIs are controlled

• Barrier methods → condoms → prevent exchange of fluids

• Regular testing → early detection + treatment → prevents spreading to others

• Education → teach about safe sex