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The Biological Importance of Water
B
io
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actsheet
September 1998 Number 30
1
Water is a polar molecule i.e. it has both positively charged and negatively
charged areas. Water is made up of two positively charged hydrogen atoms
and one negatively charged oxygen atom (Fig 1).
Plant Adaptations to Dry Environments
Xerophytes are plants which are adapted to live in dry conditions. Xeromorphic features are those which minimise water loss from the
plant. The vast majority of the water which plants absorb via their roots is lost as water vapour from the aerial parts of the plant. This loss
of water vapour is known as transpiration and is an inevitable consequence of the large moist surface area of cells which is exposed to
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1
B
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actsheet
January 1998 Number 12
Respiration
Aerobic respiration can be divided into four stages:
1. Glycolysis (G)
2. The Link reaction (LR)
3. Kreb?s cycle (K)
4. The electron transfer chain (ETC)
These take place in different parts of the cell (Table 1) and the detailed
biochemistry of these reactions is shown overleaf.
The Cell Surface Membrane
B
io
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actsheet
September 1997 Number 8
1
The cell surface membrane (formerly called the plasma membrane) surrounds the cytoplasm of eukaryotic cells. The membrane forms
a selectively permeable barrier, controlling the substances that enter and leave the cell and therefore enables the cell to regulate its
internal environment.
1
B
io
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actsheet
September 1997 Number 4
Structure to function in eukaryotic cells
The cell surface membrane and the membranes which form organelles in
eukaryotic cells all have the same basic structure, known as the fluid
mosaic model. Such membranes provide control of the entry and exit of
substances into cells and organelles and such control is a result of the
phospholipid bilayer and membrane proteins.
1
B
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actsheet
September 1997 Number 1
The kidney: excretion and osmoregulation
Kidneys have two main functions.
1. They are excretory organs, removing nitrogenous and other waste from the body.
2. They play an important part in maintaining a constant internal environment by helping to regulate pH, water and sodium ion
concentrations in the blood and tissues. This Factsheet will focus on the role of the kidney in excretion and osmoregulation.
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APUSH
Writing the Document-Based Question (DBQ)
The APUSH exam format includes one document-based question. Students will have 55 minutes to answer it.
Radioactive Decay
Activation Energy (Ea): The threshold energy that must be overcome to produce a chemical reaction
Electromagnetic Radiation: Radiant energy that exhibits wavelike behavior and travels through space at the speed of light in a vacuum
Radioisotope: a radioactive isotope
Many nuclei are radioactive
Radioactive: Refers to a nucleus that spontaneously decomposes to form a different nucleus
Over 85% of all known nuclides are radioactive
Nuclear Equation: an equation representing radioactive decay
Water?s Changes of State
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