Cells as the basic structural unit of all living organisms
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Question
State the three points of cell theory.
Answer
All living things are made of **cells**; the **cell is the basic unit** of life; new cells come only from **pre-existing cells**.
Question
Define spontaneous generation.
Answer
The (disproved) idea that living organisms can form from **non-living material**.
Question
How did Pasteur disprove spontaneous generation?
Answer
Broth in a **swan-neck flask** stayed clear; only when the neck was **broken** (letting air-borne microbes in) did it go cloudy — so cells come from cells.
Question
What does cell theory say is the smallest unit of life?
Answer
The **cell** — there is no smaller living unit.
Question
List the seven functions of life.
Answer
**Metabolism, Reproduction, Sensitivity, Growth, Respiration, Excretion, Nutrition** (MRS GREN).
Question
What is the memory aid for the functions of life?
Answer
**MRS GREN**.
Question
Define excretion.
Answer
The removal of the **waste products of metabolism** from a cell or organism.
Question
Define nutrition.
Answer
Taking in (or making) the **food and nutrients** an organism needs.
Question
What is a unicellular organism?
Answer
An organism made of a **single cell** that carries out **all seven functions of life** by itself.
Question
Why must a single cell perform all functions of life?
Answer
It is a complete organism with **no other cells to help**, so that one cell must do every job needed to stay alive.
Question
Why must even a single cell excrete?
Answer
Its **metabolism produces waste** (e.g. CO₂) that would **build up and become toxic** if not removed.
Question
Which function of life is 'responding to stimuli'?
Answer
**Sensitivity**.
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Topic 1.4 hub
Cell structure
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