Mice (Mus musculus) have various defence systems against predators such as foxes (Vulpus vulpus) or stoats (Mustela erminea). The mice release specific alarm compounds when under threat that serve as danger signals for other mice. Predators also release scents that the mice can detect.

In one study, mice were exposed to paper soaked in compounds taken from other mice, foxes or stoats in a test chamber. The scientists then measured the reaction of three different groups of neurons used in smelling: G1, G2 and G3, as shown in the diagram.

The percentage of G1, G2 and G3 neurons responding to the mouse, fox and stoat compounds, as well as a control compound, are shown in the chart.

Antiretroviral drugs are used to treat Human Immunodeficiency Virus (HIV) infections. Zidovudine (ZDV) and nevirapine (NVP) are examples of antiretroviral drugs. There are concerns that these drugs may be toxic to body cells in mitosis. In a study using Allium cepa, root tips were exposed to the drugs for 96 hours at a range of concentrations. The control treatment was a drug concentration of $0 \mu \mathrm{~mol}$. In the graph, root lengths after the 96-hour treatment period are expressed as a percentage of the length of the control.

In winter when temperatures drop, brown bears (Ursus arctos) enter a cave and hibernate. The graph shows the mean values for the body temperature, heart rate and activity of 14 brown bears throughout the year. The grey shaded areas indicate the periods when the bears are in transition between hibernation and normal activity.

In an experiment to determine the effect of diet on response to leptin, mice were fed a control diet or a high fructose diet for six months and then either injected with a saline (salt) solution or injected with leptin. The food intake of both groups was then monitored over a 24 hour period.
Removed for copyright reasons

Vibrio fischeri is a bioluminescent (light-producing) bacterium in the Pacific Ocean. V. fischeri grown in the laboratory often has less luminescence. An investigation was carried out to look at the effect of the external osmolarity (in mOsmol) on the bacterium's luminescence, at different densities of bacteria. V. fischeri cultures were grown in three different concentrations of artificial seawater. Relative luminescence is the total luminescence divided by the density of bacteria.

Key: osmolarity
- 1300 mOsmol
- 810 mOsmol
- 570 mOsmol

Testosterone and epinephrine (adrenaline) are two of the many hormones used for cell-to-cell communication in the human body.

The electron micrograph shows part of a pancreas cell that secretes digestive enzymes.

The pavement ant (Tetramorium caespitum) eats organic matter found within its territory. Individual ants leave their nest to forage for food. When they find a suitable source of food they return and communicate to other ants in the colony where the food can be found. The diagram shows the path of one ant when foraging for food and returning to the nest after finding food.

Honey bees (Apis mellifera) live in colonies where some workers exhibit scouting behaviour. The scouts communicate information on new food sources to the non-scouting workers of the colony.