Microscopic life in the water

Life evolved in the water (It is an easier environment to live in)

• You are never short of water so you don’t need adaptations to reduce water loss

• Water temperature hardly changes so you don’t need mechanisms of thermoregulation (like sweating)

• Water provides a lot of support so you don’t need a strong skeleton

• Waste products are easily got rid of

There are some problems

• Osmosis: specially a problem in freshwater (think)

• Viscosity makes it harder to move through (think of a solution)

• Water contains less oxygen than the air

Solving osmosis problems

• Water entry is not a problem for plants (Why?)

• Water constantly crosses animal cell membranes by osmosis

• Sometimes a waterproof skin is not practical

• Amoeba has a contractile vacuole

• Water is pumped into the vacuole, which increases in size

• Eventually it goes to the surface and bursts

Fish on the move

• Salmon and eels move from saltwater to freshwater

• In the sea water leaves and salt enters

• In rivers water enters • They have adapted

their kidneys and gills to cope

Salmon kidneys• Able to produce very concentrated urine containing very

little water when in the sea• Produce large amounts of very dilute urine in rivers

Salmon gills

• At sea, special cells in the gills pump out sodium and chloride ions using active transport.

• In rivers the active transport switches round to the other direction

Some animals are adapted to both

• E.g. frogs• Some have aquatic

and terrestrial stages of their life cycle

• E.g. insects and frogs

Metamorphosis

• Total change in body shape

• Allows adult and larva to live in different environment

• Reduces competition between adult and larva

Plankton

• Plankton with cell walls and chlorophyll is called phytoplankton (also called algae)

• Plankton with no cell wall or chlorophyll is called zooplankton

• Phytoplankton (obviously) do photosynthesis.

Algal blooms• Phytoplankton

change in numbers depending on– Temperature

• So changes are seasonal

– Concentration of nitrates and phosphates

• what are these used for?

• A large explosion in population is called an algal bloom

Eutrophication

• Fertilizer/sewage in water increases nitrate/phosphate concentration

• Algae grow rapidly (algal bloom)

• Increased competition means lots of dead algae

• Decomposers break down dead algae and use up oxygen while doing respiration

• Fish die due to lack of oxygen

Biological pollution indicators

• Some species need high oxygen concentrations and low levels of pollution to survive– E.g. mayfly larva

• Others can tolerate high levels of pollution and low levels of oxygen– E.g. blood worm

• Some species can tolerate acidic environments and can be used to test for….?

PCBs and DDT

• PCBs are chemicals that were used extensively in various industries

• DDT is a pesticide• They do not break

down in the environment

Bioaccumulation

• Chemicals flow, leach or are blown into the water

• They enter the bodies of aquatic plants and animals

• Consumers eat many organisms that contain these chemicals

• Top predators consume the highest levels

• PCBs affect reproduction• Seals and whales are

effected. And…?