Freshwater Habitat – SS1 Biology Lesson Note (Third Term)

A freshwater habitat is a body of water formed mainly from inland waters that contains very low or no salt. It is of two types based on movement: lotic (running water, such as rivers, springs and streams) and lentic (still water, such as lakes, ponds and dams).

Behavioural objectives

By the end of the lesson, students should be able to:

• define a freshwater habitat and state its two types, with examples;
• list the characteristics of freshwater habitats;
• name some plants and animals of freshwater habitats;
• describe the adaptive features of these plants and animals;
• write examples of food chains in freshwater habitats.

What is a freshwater habitat?

A freshwater habitat is a body of water formed mainly from inland waters. It contains very low or no salt. Fresh water is of two types based on its mobility:

1. Lotic fresh waters: These are running waters flowing continuously in a specific direction, for example rivers, springs and streams.
2. Lentic fresh waters: These are stagnant waters which do not flow, for example lakes, ponds, puddles, swamps and dams.

What are the characteristics of freshwater habitats?

1. It contains little or no salt. Salinity is 5 parts per thousand, i.e. 0.5%.
2. It is small in size.
3. Oxygen concentration is high, being available in all parts of the water body, especially at the surface.
4. The water is shallow, so sunlight penetrates to the bottom.
5. The temperature varies with seasons and depth.
6. It has seasonal variation: it decreases or dries up in the dry season and increases in the rainy season.
7. Water currents affect the distribution of organisms, salts and gases, especially in lotic fresh waters.

How are plants distributed and adapted in fresh water?

Plants of fresh water include water lilies, spirogyra, water lettuce, water weeds and others. They have the following adaptive features:

1. Water lily has:
   • an air bladder;
   • expanded tips and a light weight, which keep it afloat.
2. Spirogyra has a mucilaginous cover for protection.
3. Water lettuce has hairs on its leaves to trap air and keep it afloat.
4. Water weed (elodea) has a long and flexible petiole for swinging with water currents.

How are animals distributed and adapted in fresh water?

Animals of freshwater habitats include protozoa, ducks, pond skaters, hydra, fishes and others. Their adaptive features include:

1. Protozoa have a contractile vacuole for osmoregulation in water.
2. A duck has webbed feet for locomotion and a serrated beak for sieving food in water into its mouth.
3. Hydra has a slippery surface, hooks and suckers for attachment to water particles.
4. Pond skaters have long legs for skating on the water’s surface.
5. Fishes have swim bladders for buoyancy and gills for respiration.

What are examples of food chains in freshwater habitats?

1. Diatoms → fish fry → tilapia
2. Spirogyra → tadpoles → carps → kingfish
3. Algae → mosquito larva → small fish

Evaluation

1. Define a freshwater habitat.
2. Name the two types of fresh water and give two examples of each.
3. State four characteristics of freshwater habitats.
4. Describe one adaptive feature each of the water lily, the duck and the pond skater.
5. Write one food chain that ends with tilapia.

Assignment

1. List three plants of freshwater habitats and state one adaptive feature of each.
2. List three animals of freshwater habitats and state one adaptive feature of each.
3. Explain why oxygen concentration is high in freshwater habitats.