Download BIOLOGY 2a SUMMARY SHEET - Downlands Community School

BIOLOGY 2a SUMMARY SHEET
B2.1.1 CELLS
Most human and animal cells have the following parts.
 NUCLEUS – controls the activities of the cell
 CYTOPLASM – where most of the chemical reactions take place
 CELL MEMBRANE – controls the passage of substances into and out of the cell
 MITOCHONDRIA – responsible for releasing energy in respiration
 RIBOSOMES – responsible for protein synthesis (making proteins)
Plant and algal Cells have all the above but also have:
 CELL WALL, made of cellulose– which strengthens the plant cell
 PERMANENT VACUOLE – full of cell sap which pushes against the cell wall to give
support.
 CHLOROPLASTS – absorb light energy to make food.
Animal Cell
Plant Cell
A Bacterial cell has:
 cytoplasm,
 a membrane surrounded by a cell wall.
 The genes are not in a distinct nucleus
Yeast is a single celled organism. Yeast cells have:
A nucleus, Cytoplasm, A membrane surrounded by a cell wall
Specialised Cells
Different types of cells look different because they are adapted to their function. They
are said to be specialised.
2.1.2 DIFFUSION
Dissolved substances get into and out of cells by diffusion.
This is the spreading of the particles of a gas, or any substance in a solution, from an
area of high concentration to one of low concentration. In other words it is trying to
even up any differences in concentration.
For example if you take the top off a perfume bottle there will be a smell of perfume
close to the bottle. The perfume particles (and hence the smell) will gradually spread
around the room. Eventually the smell will be the same everywhere in the room.
Diffusion is fastest when there is a large difference in concentration (big concentration
gradient)
Oxygen for respiration passes through cell membranes by diffusion.
2.2 TISSUES, ORGANS and ORGAN SYSTEMS
Large organisms are made of many cells. To help them work effectively the cells
differentiate and become adapted to carry out specific functions as the organism
develops.
A tissue is a group of cells with a similar structure and function. Examples are:
 Muscular tissue, which can contract to cause movement
 Glandular tissue, which can produce substances such as enzymes and hormones
 Epithelial tissue, which covers some parts of the body
Organs are made of tissues, usually several types working together. The stomach is an
organ which contains:
 Muscular tissue, to churn the contents
 Glandular tissue, to produce digestive juices
 Epithelial tissue, to cover the outside and inside of the stomach.
Organ Systems are groups of organs that work together. The digestive system is one
example. It includes:
 Glands, such as the pancreas and salivary glands, which produce digestive juices
 The stomach and small intestine, where digestion takes place
 The liver, which produces bile
 The small intestine, where absorption of soluble food occurs
 The large intestine, where water is absorbed from undigested food, producing
faeces
You should be able to recognise the organs of the digestive system on a diagram
B2.2.2 PLANT ORGANS.
Plant organs include the stem, roots and leaves. You need to know the internal structure
of a leaf
Plant tissues include:
 Epidermal tissues, which cover part of the plant
 Mesophyll, which carries out photosynthesis
 Xylem and phloem, which transport substances around the plant.
B2.3.1 PHOTOSYNTHESIS
Green plants use light energy to make their own food. They obtain the raw materials they
need to make this food from the air and the soil.
During photosynthesis: light energy is absorbed by a green substance called chlorophyll which is found in
chloroplasts in some plant cells and algae
 this energy is used to convert carbon dioxide (from the air) and water (from the
soil) into sugar (glucose)
 oxygen is released as a by-product.
This is summarised by the equation:carbon dioxide + water (+ light energy)  glucose + oxygen
The glucose produced during photosynthesis is used in the following ways:
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Plant cells respire using some of the glucose.
Some of the glucose may be converted into insoluble starch for storage.
To produce fat or oil for storage
To produce cellulose which strengthens the cell wall
To produce proteins – Proteins also need Nitrogen. Plants get this from soluble
nitrate ions dissolved in the water from the soil.
LIMITING FACTORS
The rate of photosynthesis may be limited by:- low temperature;
- shortage of carbon dioxide
- shortage of light
These three things interact and in practice any one, or a combination of them, may be
the factor that limits photosynthesis.
You should be able to interpret data (e.g. graphs) showing how factors affect the rate
of photosynthesis and evaluate the benefits of artificially changing the environment in
which plants are grown.
e.g. Greenhouses are used to grow tomatoes. They are lit and heated 24 hours a day to
maximise growth but this is a waste if there is not enough carbon dioxide for the plants
to use.
B2.4.1 ORGANISMS AND THEIR ENVIRONMENT
Living organisms form communities that have complex relationships. These can be
affected by external factors.
You should be able to:
 suggest the reasons for the distribution of organisms in a habitat
 evaluate methods used to collect environmental data including the validity of the
method and reproducibility of the data as evidence for environmental change.
 Understand the terms mean, median and mode.
 Understand that sample size is related to validity and reproducibility.
Physical factors that affect the distribution of organisms:
 Temperature
 Availability of nutrients
 Amount of light
 Availability of water
 Availability of oxygen and carbon dioxide
Data on the distribution of organisms can be obtained by:
 Random sampling with quadrats
 Sampling along a transect