Biology B4, B5, B6 OCR 21st century

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B4 ­ The Processes of Life

B4.1 How do chemicals reactions take place in living things

All living cells are made from basic units ­ these are called CELLS.

The processes of life carried out by all living cells depend on chemical reactions within cells ­ these
reactions need energy…

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For enzymes to work to their optimum they need a specific and constant temperature:

Different enzymes have different optimum
working temperatures. For example, in the
human body enzymes work best at 37°C .
Below this temperature their rate of action
slows down however, if the temperature gets
too high the…

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B4.2 How do plants make food?

Photosynthesis can be written as

C arbon dioxide + W ater Glucose + Oxygen

The equation can also be written like this:

6CO2 + 6H2O C6H12O6 + 6O2

There are three main stages in photosynthesis:

Light energy is absorbed by the green chlorophyll

Energy…

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Plants need other chemicals in addition to glucose. The roots take up minerals from the soil in
solution. Nitrogen, in the form of nitrates is absorbed and used by plant cells to make proteins.

Substances move through cells via the process of DIFFUSION. Diffusion is the overall movement of a…

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There are several factors that can limit the rate the rate of photosynthesis:

Temperature ­ too low and photosynthesis stops until the temperature rises again. Too high
and the enzymes stop working permanently
Carbon dioxide concentration ­ as carbon dioxide concentration increases, so does the
rate of photosynthesis
Light intensity…

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AEROBIC RESPIRATION releases energy through the breakdown of glucose molecules, by combining
them with oxygen inside living cells. The majority of animal and plant cells and some microorganisms
respire aerobically.

Glucose + Oxygen Carbon dioxide + W ater + Energy released

C6H12O6 + 6O2 6CO2 + 6H2O

ANAEROBIC RESPIRATION takes…

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YEAST ­ yeast is a type of fungus ­ it is used to make bread and alcohol. Unlike bacteria yeast does
have membrane-bound organelles.




Animal cell Bacteria Yeast

Cytoplasm


Cell membrane

Mitochondria

Nucleus


Ribosomes


Cell wall

Circular DNA



Applications of Anaerobic respiration ­ Biotechnology has enabled us to use the…

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Anaerobic respiration ­ this takes place in the absence of oxygen. The yeast respires anaerobically
and produces alcohol and carbon dioxide instead of multiplying

Biogas ­ It is now possible to introduce bacteria to biodegradable substances such as manure,
sewage and household waste in landfill sites. The anaerobic digestion leads…

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B5 ­ Growth and development

B5.1 How do organisms develop

Cells are the building blocks of all living things ­ multicellular organisms are made up of collections
of cells. The cells can become specialised to do a particular job.

Groups of specialised cells working together are called tissues and a…

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