Biology B4, B5, B6 OCR 21st century

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  • Created on: 28-09-14 17:41
Preview of 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 released by RESPIRATION (the release energy from food). RESPIRATION is
one of seven major life processes:
All living things move ­ to find food, escape predators or find better growing
M Movement
R Respiration Getting energy from food to carry out cell processes
S Sensitivity Detecting changes in the surroundings such as light levels
G Growth All living things grow
Reproductio Making new generations of a species
E Excretion Getting rid of waste ­ including carbon dioxide from respiration
N Nutrition Taking in and using food as a supply of energy
PHOTOSYNTHESIS ­ makes food molecules and energy available to living organisms through food
Photosynthesis can be summarised by saying that carbon dioxide and water are combined to
produce sugar and oxygen in the presence of light and chlorophyll.
Photosynthesis uses sunlight to build large molecules in plant cells and some microorganisms (e.g.
Enzymes are biological catalyst; they are proteins that speed up chemical reactions. Cells make
enzymes according to the instructions carried in genes. Enzymes are specific so only molecules with
the correct shape can fit into the enzyme ­ this is called the lock and key model.
Once the enzyme and molecule (substrate) are linked the reaction takes place, the products are
released and the process is able to start again.

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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 enzyme is DENATURED and stops
The biological name for the process of permanent change in an enzyme's shape is denaturing. The
place where the substrate fits to the enzyme is called the ACTIVE SITE.…read more

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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 used to bring about the reaction between carbon dioxide and water to produce glucose (a
Oxygen produced as a waste product
Glucose is made up of carbon, hydrogen and oxygen atoms.…read more

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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
substance from a region where it is in high concentration to an area where it is in lower concentration.
Diffusion is a passive process as it does not need an energy input to happen.…read more

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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 ­ light is needed for photosynthesis. The greater the availability of light the
quicker photosynthesis will take place
To identify the effect of light on plants, biologists have to carry out fieldwork.…read more

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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 place in conditions of low oxygen or absence of oxygen to include:
Animals cells (e.g. in humans during vigorous exercise)
Plant cells (e.g.…read more

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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
Cell membrane
Cell wall
Circular DNA
Applications of Anaerobic respiration ­ Biotechnology has enabled us to use the products of
anaerobic respiration
Making bread ­ Yeast is added to a dough, made from flour, salt, water and other ingredients.…read more

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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 to the production of
methane (an explosive gas) and carbon dioxide. The methane can be used as a low-cost fuel.…read more

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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 group of tissues working
together are called organs.
When an egg is fertilised by a sperm it becomes a ZYGOTE.…read more



THIS IS AMAZING! I somehow cannot download your B1, B2, B3 summary - can you please sort that out so that I can access that too! 




I cannot thank you enough for the amount of time you have saved me!

Thank You!

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