Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Unit 7: Genes and inheritance

GRADE 8 – Unit 7: Genes and inheritance — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 9 parts Lesson 1 of 9 1 quiz

📚 HIA International - Grade 8 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

GRADE 8 - Unit 7: Genes and inheritance — HIA INTERNATIONAL notes: Describe microorganisms and decomposers, food chains, fermentation, DNA and chromosomes, sex determination and natural selection.Groups — bacteria, fungi and viruses.Decomposers — mainly bacteria and fungi, which …

  • Respiration
  • Bioaccumulation
  • Investigating
  • Decomposers — mainly bacteria and fungi, which break down dead organisms and waste such as faeces; this is decay
  • Enzymes — they release enzymes onto dead material to digest it into small soluble molecules, which they absorb
  • Recycling — mineral ions such as nitrates return to the soil and carbon returns to the air

Part 1 of 7Microorganisms and decay

Microorganisms and decay
Groups
  • Groups bacteria, fungi and viruses.
Decomposers
  • Decomposers mainly bacteria and fungi, which break down dead organisms and waste such as faeces;
    • this is decay.
Enzymes
  • Enzymes they release enzymes onto dead material to digest it into small soluble molecules, which they absorb.
Respiration
  • Respiration decomposers respire, releasing carbon dioxide into the air.
Recycling
  • Recycling mineral ions such as nitrates return to the soil and carbon returns to the air.
Speed
  • Speed decay is fastest when it is warm and moist.
Bioaccumulation
  • Bioaccumulation toxic chemicals such as some pesticides build up along a food chain and harm top predators most.

Part 2 of 7Roles in a food chain

RoleGets energy fromExample
ProducerSunlight (photosynthesis)Grass
Primary consumerProducersRabbit (herbivore)
Secondary consumerPrimary consumersFox (carnivore)
Tertiary consumerSecondary consumersEagle
DecomposerDead organismsFungi, bacteria

Part 3 of 7Useful microorganisms and fermentation

Fermentation
Fermentation the breakdown of sugar by microorganisms without oxygen: sugar → ethanol + carbon dioxide.
Bread
  • Bread yeast respires sugar in the dough, producing carbon dioxide bubbles that make dough rise;
    • baking kills the yeast and evaporates the ethanol.
Brewing
  • Brewing the same reaction produces ethanol.
Dairy
  • Dairy bacteria turn milk sour to make yoghurt and cheese; pasteurisation kills harmful microbes.
Investigating
  • Investigating vary temperature, measure gas volume or bubbles, and control sugar, yeast and volume.

Part 4 of 7DNA and chromosomes

1Chromosome
Chromosome a long coiled thread of DNA found in the nucleus.
2Gene
  • Gene a section of DNA that controls a characteristic.
3Gametes
  • Gametes sex cells with half the chromosome number.
    • (23 in humans, 46 in other cells)
4History
  • Rosalind Franklin’s X-ray images of DNA helped James Watson and Francis Crick build the double helix model in 1953, with Maurice Wilkins.
5Science
  • Science shows scientists building on each other’s evidence.

Part 5 of 7Sex determination

Mother
  • Mother has XX chromosomes and all eggs carry X.
Father
  • Father has XY, and sperm carry either X or Y.
Girl
  • Girl an X sperm fertilising an egg gives XX.
Boy
  • Boy a Y sperm gives XY.
Chance
  • 2 of 4 combinations (XX, XX, XY, XY) are XY, so a 50% (1 in 2) chance of a boy.

Part 6 of 7Variation

Variation
Variation differences between individuals of the same species.
Causes
  • Causes genes inherited from both parents, and the environment.
Result
  • Result offspring resemble, but are not identical to, either parent.

Part 7 of 7Natural selection and evolution

1
Individuals in a population show variation because of differences in their genes.
2
More offspring are born than can survive, so there is competition for food, space and mates.
3
Individuals with characteristics that suit the environment are more likely to survive.
4
They breed and pass on the genes for these characteristics.
5
Over many generations the useful characteristic becomes more common.
Evolution
  • Evolution this change over time can lead to new species.
Examples
  • Examples antibiotic-resistant bacteria and peppered moths.

Key terms

TermMeaning
DecomposerAn organism, mainly bacteria and fungi, that breaks down dead organisms and waste.
DecayThe breaking down of dead organisms and waste by decomposers.
FermentationBreakdown of sugar by microorganisms without oxygen.
ChromosomeA long coiled thread of DNA found in the nucleus.
GameteA sex cell with half the chromosome number.
Natural selectionThe process by which individuals better suited to their environment survive and breed.
EvolutionChange in a population’s characteristics over many generations.
BioaccumulationThe build-up of toxic chemicals along a food chain.

Avoid these mistakes

1
Thinking all microorganisms are harmful — decomposers and yeast are useful.
2
Saying baking makes the bread rise — yeast produces carbon dioxide before it is killed.
3
Saying the father decides sex by passing X only — he passes X or Y, giving a 50% chance of a boy.
4
Saying individuals evolve during their lifetime — populations change over many generations.
5
Saying chromosomes are in the cytoplasm — they are in the nucleus.

Last updated: