Pearson Edexcel International GCSE Science Single Award 1: Biology: The nature and variety of living organisms

This topic establishes what living organisms do and how major groups differ. The 4SS0 Single Award boundary consists of points 1.1 to 1.4: shared life characteristics, eukaryotic groups, bacteria, pathogens and viruses. It is narrower than using a general classification chapter from another qualification.

Characteristics of living organisms

Living organisms require nutrition, respire, excrete waste, respond to surroundings, move, control internal conditions, reproduce, and grow and develop. These characteristics work together rather than serving as a checklist where one observation always proves life.

Nutrition supplies materials and energy sources. Respiration releases usable energy from organic substances. Excretion removes metabolic waste, such as carbon dioxide or urea, rather than undigested food. Response involves detecting and reacting to stimuli. Movement can occur in whole organisms or parts. Control of internal conditions maintains a suitable internal environment. Reproduction generates new organisms, while growth and development involve lasting changes.

Dormant seeds may show little visible activity yet remain living. Fire can spread and consume fuel but lacks cellular organisation and inherited biological reproduction. Classification must therefore use the combined evidence.

Plants and animals

Plants are multicellular eukaryotes. Their cells contain chloroplasts for photosynthesis, cellulose cell walls and usually large vacuoles. They store carbohydrate as starch or sucrose. Required examples include a cereal such as maize and a herbaceous legume such as peas or beans.

Animals are multicellular eukaryotes without chloroplasts or cell walls. They usually have nervous coordination and can move from place to place. They often store carbohydrate as glycogen. Mammals such as humans and insects such as houseflies and mosquitoes illustrate the group.

Not every plant cell contains chloroplasts: root cells normally do not. The group description concerns the organism and its characteristic tissues, not an assertion that every cell is identical.

Fungi and protoctists

Fungi do not photosynthesise. A typical multicellular fungus has a mycelium of thread-like hyphae that may contain many nuclei. Fungal cell walls contain chitin. Fungi feed saprotrophically by secreting digestive enzymes onto organic material and absorbing the soluble products. They may store glycogen.

Mucor demonstrates hyphal organisation, while yeast is single-celled. Calling every fungus a plant ignores its nutrition, wall material and storage carbohydrate.

Protoctists are mainly microscopic single-celled eukaryotes. Amoeba has animal-like features. Chlorella contains chloroplasts and is plant-like. Plasmodium is a pathogenic protoctist that causes malaria. “Animal-like” and “plant-like” describe features; they do not place these examples inside the animal or plant kingdoms.

Bacteria

Bacteria are microscopic single-celled prokaryotes. They have a cell wall, cell membrane and cytoplasm. They contain a circular DNA chromosome and may contain plasmids, but they lack a nucleus.