BIOLOGY UNIT 1

What does MRS GREN stand for?

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition (plus Control of internal conditions – homeostasis)

Define nutrition in living organisms

The process by which organisms obtain food (nutrients) for energy, growth, and repair

How do plants obtain nutrition?

Make their own food by photosynthesis (autotrophic nutrition)

How do animals obtain nutrition?

Eat other organisms (heterotrophic nutrition)

How do fungi obtain nutrition?

Absorb nutrients from dead or decaying matter (saprotrophic nutrition)

Define respiration

The chemical process that releases energy from glucose inside living cells. Occurs in all living cells at all times

Is respiration the same as breathing?

No. Respiration = chemical reaction in cells. Breathing = mechanical movement of air in/out of lungs

Write the word equation for aerobic respiration

Glucose + Oxygen → Carbon dioxide + Water (+ energy)

Give 4 uses of the energy released by respiration

Muscle contraction (movement), protein synthesis (growth/repair), active transport, cell division, maintaining body temperature (any 4)

Define excretion

The removal from the body of metabolic wastes (waste products from chemical reactions inside cells)

Is faeces excretion?

No. Faeces is egestion (removal of undigested food that never entered cells)

What waste product is produced by respiration and excreted by the lungs?

Carbon dioxide

What waste product is produced by breakdown of excess proteins and excreted by the kidneys?

Urea

Define sensitivity (response to surroundings)

The ability to detect and respond to changes in the environment (stimuli)

Give one example of a plant response

Shoot grows towards light (phototropism) OR root grows towards water (hydrotropism) OR root grows downwards with gravity (gravitropism)

Give one example of an animal response

Moves away from danger or towards food

Define movement in living organisms

A change in position or place of the whole organism or part of the organism

Can plants move?

Yes – they move parts of their body (e.g., flowers closing, shoots growing towards light) but do NOT move whole body

What is the key difference between movement in animals and plants?

Animals move whole body (locomotion); plants move parts (usually by growth)

Define homeostasis

Maintaining a constant internal environment despite external changes (controlling internal conditions)

Give 3 examples of conditions controlled by homeostasis

Body temperature, blood glucose level, water and salt balance (osmoregulation), blood pH (any 3)

Why is homeostasis important?

Allows enzymes to work at optimum conditions so metabolic reactions proceed efficiently

Define reproduction

The process of producing offspring to ensure the survival of the species

What is the difference between asexual and sexual reproduction?

Asexual: one parent, offspring genetically identical (clones). Sexual: two parents, offspring genetically different

Is reproduction essential for survival of an individual?

No – but essential for survival of the species

Define growth

A permanent increase in size and dry mass (mass with all water removed)

Define development

Change in shape or form as an organism matures (e.g., tadpole → frog)

What is the most reliable way to measure growth?

Dry mass (not wet mass, because water content varies)

What 2 processes are involved in growth?

Cell division (mitosis) and cell enlargement

What is a eukaryotic organism?

An organism whose cells contain a true nucleus (DNA enclosed in a nuclear membrane) and membrane-bound organelles

What are the 4 eukaryotic kingdoms in IGCSE?

Plants, Animals, Fungi, Protoctists

Give 6 features of plants

Multicellular, chloroplasts present, photosynthesis (autotrophic), cellulose cell wall, store carbohydrate as starch/sucrose, cannot move whole body (only parts)

What carbohydrate do plants store?

Starch (in storage organs) or sucrose (transport)

What is plant cell walls made of?

Cellulose

Give two examples of plants from the syllabus

Flowering plants: cereal (e.g., maize) and herbaceous legume (e.g., peas or beans)

Give 7 features of animals

Multicellular, no chloroplasts, cannot photosynthesise (heterotrophic), no cell wall, usually have nervous co-ordination, can move whole body, store carbohydrate as glycogen

What carbohydrate do animals store?

Glycogen (in liver and muscles)

Do animals have a cell wall?

No – only cell membrane

Give two examples of animals from the syllabus

Mammals (e.g., humans) and insects (e.g., housefly, mosquito)

Give 7 features of fungi

Most multicellular (except yeast), no chloroplasts, cannot photosynthesise (heterotrophic), cell wall made of chitin, body organised into mycelium of hyphae, hyphae contain many nuclei, saprotrophic nutrition, store carbohydrate as glycogen (any 7)

What are fungal cell walls made of?

Chitin (NOT cellulose)

What is a mycelium?

A network of thread-like structures called hyphae

What is saprotrophic nutrition?

Secreting digestive enzymes extracellularly onto dead/decaying food, then absorbing the digested organic products

List the 5 steps of saprotrophic nutrition

Hyphae grow over dead/decaying matter, digestive enzymes secreted onto food, enzymes digest food externally into soluble products, soluble products absorbed through hyphal wall/membrane, nutrients used for energy and growth

What carbohydrate do fungi store?

Glycogen

Give two examples of fungi from the syllabus

Mucor (has hyphae) and yeast (single-celled)

Is yeast multicellular or single-celled?

Single-celled (unicellular)

Give 3 features of protoctists

Microscopic single-celled, have a true nucleus (eukaryotic), some like animal cells, some like plant cells

Which protoctist is animal-like and moves using pseudopodia?

Amoeba

Which protoctist is plant-like and has chloroplasts?

Chlorella

Which protoctist causes malaria?

Plasmodium

What is the vector for malaria?

Anopheles mosquito

Name 3 features of Amoeba

No chloroplasts, no cell wall, moves using pseudopodia, feeds on other organisms (heterotrophic), lives in pond water (any 3)

Name 3 features of Chlorella

Has chloroplasts, photosynthesises (autotrophic), has a cell wall, lives in fresh water (any 3)

Do all protoctists photosynthesise?

No – Amoeba and Plasmodium do not

What is the common exam mistake about protoctists?

Calling them "simple" – examiners prefer "single-celled" or "unicellular"

What is the common exam mistake about growth?

Saying growth is just "getting bigger" – must mention increase in dry mass

What is the common exam mistake about fungi cell walls?

Saying fungi have cellulose cell walls – wrong, they have chitin

What is the common exam mistake about excretion and faeces?

Saying faeces is excreted – wrong, faeces is egestion, not excretion

What is the common exam mistake about plants moving?

Saying plants "do not move" – wrong, plants move parts (tropisms)

What is the common exam mistake about all fungi being multicellular?

Wrong – yeast is single-celled

What is the common exam mistake about all cells having a nucleus?

Wrong – prokaryotes (bacteria) do not have a true nucleus

Quick comparison: Do plants have chloroplasts?

Yes

Quick comparison: Do animals have chloroplasts?

No

Quick comparison: Do fungi have chloroplasts?

No

Quick comparison: Do protoctists have chloroplasts?

Some yes, some no

Quick comparison: Do plants have a cell wall?

Yes (cellulose)

Quick comparison: Do animals have a cell wall?

No

Quick comparison: Do fungi have a cell wall?

Yes (chitin)

Quick comparison: Do protoctists have a cell wall?

Some yes, some no

Quick comparison: What carbohydrate do plants store?

Starch/sucrose

Quick comparison: What carbohydrate do animals store?

Glycogen

Quick comparison: What carbohydrate do fungi store?

Glycogen

Quick comparison: What is the nutrition type of plants?

Autotrophic (photosynthesis)

Quick comparison: What is the nutrition type of animals?

Heterotrophic (ingestion)

Quick comparison: What is the nutrition type of fungi?

Saprotrophic (external digestion)

Quick comparison: Are plants multicellular?

Yes

Quick comparison: Are animals multicellular?

Yes

Quick comparison: Are fungi multicellular?

Usually (except yeast)

Quick comparison: Are protoctists multicellular?

No (single-celled)

What is a prokaryotic organism?

An organism whose cells lack a true nucleus (no nuclear membrane). DNA is free in the cytoplasm as a circular chromosome. Also lacks membrane-bound organelles (no mitochondria, no chloroplasts, no ER)

What are the only prokaryotes you need to know for IGCSE 4BI1?

Bacteria

Are bacteria multicellular or unicellular?

Unicellular (single-celled) and microscopic

Do bacteria have a true nucleus?

No – they have no true nucleus. DNA is a circular chromosome free in the cytoplasm

What is the size range of bacteria?

Microscopic – typically 0.5–5 micrometres (much smaller than eukaryotic cells)

Do bacteria have a cell wall?

Yes – but made of peptidoglycan/murein (NOT cellulose like plants, NOT chitin like fungi)

Do bacteria have plasmids?

Yes – small circular loops of DNA separate from the main chromosome. Plasmids carry extra genes (e.g., antibiotic resistance)

Where is the DNA located in a bacterial cell?

Free in the cytoplasm as a circular chromosome (not enclosed in a nucleus)

Do bacteria have chloroplasts?

No – even photosynthetic bacteria have chlorophyll in the cell membrane or chromatophores, NOT in chloroplasts

Do bacteria have mitochondria?

No – bacteria lack all membrane-bound organelles

What is the nutrition of most bacteria?

Heterotrophic – feed off other living or dead organisms. Only a few are photosynthetic

Name the three shapes of bacteria.

Rod-shaped (bacillus), spherical (coccus), spiral (spirillum)

Which rod-shaped bacterium is used in yoghurt production?

Lactobacillus bulgaricus (bacillus)

Which spherical bacterium causes pneumonia?

Pneumococcus (Streptococcus pneumoniae) – coccus

What does Lactobacillus bulgaricus convert lactose into?

Lactic acid (by fermentation)

Describe the 6 steps of yoghurt production using Lactobacillus.

Milk pasteurised (heated to kill unwanted bacteria), Lactobacillus added (inoculation), incubated at ~40°C (anaerobic), bacteria ferment lactose → lactic acid, lactic acid lowers pH causing milk proteins to coagulate → yoghurt thickens, yoghurt cooled to stop bacterial growth

What disease does Pneumococcus cause?

Pneumonia (infection of the lungs)

How does Pneumococcus cause pneumonia?

Inflammatory response in alveoli → fluid accumulation → difficulty breathing

What is the key difference between prokaryotic and eukaryotic DNA?

Prokaryotes: circular chromosome free in cytoplasm + plasmids. Eukaryotes: linear chromosomes inside nucleus – no plasmids (except some yeast)

Which has smaller ribosomes: prokaryotes or eukaryotes?

Prokaryotes (70S vs 80S in eukaryotes)