Biology Key Points

The key points for every single topic in the AQA Additional Science course for Biology. Presented in a nice and colourful way!

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Biology Key Points
Cells, tissues and organs
Animal and plant cells
Most human cells, like most animal cells, contain a nucleus, cytoplasm, cell
membrane, mitochondria and ribosomes.
Plant and algal cells contain everything in an animal cell, plus many also contain
chloroplasts and a permanent vacuole filled with sap.
Plant cells are different from animal cells because they have different functions.
Bacteria and yeast
Bacteria are much smaller than plant and animal cells.
Yeast is a single-celled organism, which is different from animal and plant cells.
Specialised cells
There are many different types of cell.
Cells are specialised to carry out a particular function, e.g. fat cells, cone cells, root
hair cells and sperm cells.
The structure of a cell gives a clue to its function.
Diffusion
Dissolved substances and gases can move into and out of cells by diffusion.
Diffusion occurs more rapidly when there is a larger difference in concentration.
Tissues and organs
A tissue is a group of cells with similar structure and function.
Organs are made of several tissue types.
Organ systems
Groups of organs work together in an organ system.
The digestive system in humans is adapted to exchange substances with the
environment.
Plant organs include stems, roots and leaves.
Organisms in the environment
Photosynthesis
During photosynthesis light energy is transferred to chemical energy.
Leaves are well adapted for photosynthesis.

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Limiting factors
Plants grow best when they have enough light, carbon dioxide and water, and are
kept at a suitable temperature.
If any of these conditions are not met, the rate of photosynthesis will be limited.
How plants use glucose
Plant and algal cells produce glucose during photosynthesis.
Glucose produced in photosynthesis can be used in a variety of ways.
Plants and algae also need nitrate ions to make proteins.…read more

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Specific enzymes digest each particular food type.
Speeding up digestion
Enzymes work best in a narrow pH range.
Making use of enzymes
Microorganisms produce enzymes that we can use.
Enzymes can be used in products in the home and in industry.
High-tech enzymes
There are advantages and disadvantages to using enzymes in industry and the home.
Energy from respiration
Aerobic respiration
Aerobic respiration is the release of energy from food when oxygen is available.…read more

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Sexual reproduction gives rise to variation.
Stem cells
Stem cells are not specialised, but can differentiate into many different types of cell
when required.
Stem cells can be used to cure some disorders.
From Mendel to DNA
Gregor Mendel worked out how characteristics are inherited.
Genes make up the chromosomes, which control our characteristics.
Chromosomes are large molecules of DNA.
A gene is a small section of DNA.
Everyone (except identical twins) has unique DNA.…read more

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We can learn from fossils how different organisms have changed as life developed on
Earth.
Exploring the fossil evidence
The fossil record can show us how much, or how little, organisms have changed over
time.
Many species have evolved and then become extinct.
Several factors can cause extinction of a species.
More about extinction
Environmental changes over geological time can cause extinction of organisms.
A single catastrophic event can also cause extinctions.…read more

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