The whole of Unit 1 igcse Biology

Movement

• Definition: Action of muscles or slow growth in response to stimuli.

• Exam point: E.g. roots grow towards gravity or water.

• Importance: Helps avoid predators, find food or water, spread seeds.#

Respiration

• Definition: Chemical reactions that release energy from nutrients like glucose.

• Exam point: Glucose + Oxygen → CO₂ + Water + Energy.

• Importance: Provides energy for all life functions.#

Sensitivity

• Definition: Ability to detect and respond to stimuli.

• Exam point: Plants bend toward light (phototropism); animals respond to heat or sound.

• Importance: Increases survival by reacting to environmental changes.#

Control (Homeostasis)

• Definition: Maintaining a stable internal environment (e.g. body temperature, water levels).

• Exam point: Human body regulates temperature at ~37°C.

• Importance: Ensures enzymes and cells function optimally.#

Growth

• Definition: Irreversible increase in size and dry mass due to cell division.

• Exam point: Measured by changes in height, mass, or cell number.

• Importance: Enables development, repair, and maturity.#

Reproduction

• Definition: The process of producing offspring.

• Exam point: Asexual (1 parent, identical), Sexual (2 parents, variation).

• Importance: Ensures continuation of species.#

Excretion

• Definition: Removal of metabolic waste produced by chemical reactions in cells

• Exam point: CO₂ from respiration; urea from liver.

• Importance: Prevents toxic build-up inside the body.#

Nutrition

• Definition: Intake of materials for energy, growth, and repair.

• Exam point: Plants photosynthesise; animals ingest other organisms.

• Importance: Provides essential nutrients and energy.#

Plants

• Characteristics: Multicellular, cell walls (cellulose), chloroplasts, autotrophic.

• Storage: Store carbohydrates as starch.

• Example: Maize, peas.#

Animals

• Characteristics: Multicellular, no cell walls, nervous system for coordination.- Storage: Store carbohydrates as glycogen.

• Example: Humans, insects.#

Fungi

• Characteristics: Multicellular (except yeast), cell walls (chitin), no chloroplasts.

• Nutrition: Saprotrophic (external digestion with enzymes).

• Storage: Store carbohydrates as glycogen.

• Example: Yeast, Mucor.#

Protoctists

• Characteristics: Mostly unicellular, some like plants (e.g. Chlorella), others like animals (e.g. Amoeba).

• Nutrition: Mixed; some photosynthesise.

• Note: Eukaryotic cells.#

Bacteria

• Characteristics: Unicellular, prokaryotic (no nucleus), circular DNA, plasmids.

• Nutrition: Some photosynthesise, others feed off organisms.

• Example: Lactobacillus (good), Pneumococcus (causes pneumonia).#

Viruses

• Characteristics: Not living; no cellular structure; protein coat + DNA or RNA.

• Reproduction: Only inside host cells (parasitic).

• Example: HIV (AIDS), Influenza (flu), TMV (Tobacco Mosaic Virus).#

Classification question style

• Task: Use characteristics to classify unknown organisms.

• Tip: Look for cell wall, chloroplasts, nutrition type, DNA structure.#

Compare Bacteria vs Virus

• Bacteria: Living, cells with cell wall, DNA in cytoplasm.

• Viruses: Non-living, no cells, replicate only in host.#

Storage molecule differences

• Plants: Store carbs as starch.

• Animals & Fungi: Store carbs as glycogen.#

Eukaryotic vs Prokaryotic

• Eukaryotic: Has nucleus (plants, animals, fungi, protoctists).

• Prokaryotic: No nucleus (bacteria).#

Define the term 'organism'

A living thing that carries out all seven life processes (MRS GREN)#

List the seven characteristics of living organisms

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition (MRS GREN)#

Define the term 'cell'

The basic structural and functional unit of all living organisms#

Describe the features of plant cells

Contain nucleus, cytoplasm, cell membrane, cell wall, chloroplasts, and a large permanent vacuole#

Describe the features of animal cells

Contain nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes#

Name the organelle responsible for photosynthesis

Chloroplast#

What is the function of the nucleus?

Controls the activities of the cell and contains genetic material#

What is the function of mitochondria?

Site of aerobic respiration and energy release#

What is the function of ribosomes?

Site of protein synthesis#

What is the function of a cell wall?

Provides structure and support; made of cellulose in plants#

What is the function of the vacuole?

Contains cell sap and helps maintain cell structure in plant cells#

Define the term 'multicellular'

Organisms made of many cells working together#

Define the term 'unicellular'

Organisms made of only one cell#

State the kingdom that includes yeasts and mushrooms

Fungi#

Describe how fungi feed

Saprotrophic nutrition using extracellular enzymes to digest dead organic matter#

Give an example of a single-celled fungus

Yeast#

Do fungal cells have chloroplasts?

No#

Describe the structure of a typical fungus (e.g. Mucor)

Made of hyphae, which form a mycelium; have cell walls made of chitin#

State the kingdom that includes amoeba and Plasmodium

Protoctists#

Describe how amoeba obtains nutrition

Ingests and digests other organisms (like animals)#

Describe Plasmodium and its significance

A protoctist that causes malaria; a parasitic organism#

Define the term 'prokaryote'

An organism without a nucleus (e.g., bacteria)#

Describe the features of a bacterial cell

Cell wall, cell membrane, cytoplasm, plasmid DNA, circular chromosome, no nucleus#

Give an example of a pathogenic bacterium

Pneumococcus#

What disease is caused by Pneumococcus?

Pneumonia#

Describe the structure of a virus

No cellular structure, consist of genetic material (DNA or RNA) in a protein coat#

Are viruses living?

No, because they can only reproduce inside host cells and do not carry out all life processes#

Give an example of a virus that infects humans

HIV (causes AIDS)#

How does HIV affect the body?

Destroys immune system cells, leading to AIDS#

What is a pathogen?

A microorganism that causes disease#

Name the four types of pathogen

Bacteria, viruses, fungi, protoctists#

Can viruses infect all types of organisms?

Yes, including animals, plants, and bacteria#

How are protoctists different from bacteria?

Protoctists have a nucleus (eukaryotic); bacteria do not (prokaryotic)#

Define 'saprotrophic nutrition'

A type of nutrition where organisms feed on dead or decaying material by secreting enzymes#

Why are fungi important in ecosystems?

They decompose organic matter and recycle nutrients#

Compare plant and fungal cells

Both have cell walls, but plant cell walls are made of cellulose, fungal of chitin; plants have chloroplasts, fungi do not#

What do plant cells have that animal cells do not?

Cell wall, chloroplasts, large permanent vacuole#

What is the main energy storage molecule in plants?

Starch#

What is the main energy storage molecule in animals?

Glycogen#

How do animals obtain nutrition?

They ingest and digest other organisms (heterotrophic)#

Describe a key difference between viruses and other microbes

Viruses are not cellular and require a host to reproduce#

What kingdom do algae belong to?

Protoctists#

What are pathogens an example of?

Microorganisms that can cause disease#