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Life in a Swiftly Moving Stream

Mountain streams and ponds both contain fresh water.  Pond water is warm most of the year and mountain streams fed by melting snow usually ice cold. 

Ponds are stagnant and not mixed or churned as streams.  Most ponds are fed new water only by creeks or by seepage of groundwater from the surrounding land. 

Mountain streams rushes toward the valleys below and violently mixed and thrown in the air and churned by its swift flow over rocks and a lot of air.  Crystal clear in appearance for ponds are usually muddy.

Animals in Mountain Streams

(Define hypothesis) Write the term on blackboard and define.  Hypothesis is a learned or inherited idea or an educated guess.

Mountain stream larvae are streamlined/flattened and many hang on to stones and rocks as the water rushes over them.  An effective adaptation-example- caddis fly- a larva that makes a case in which it lives.  There are 400 different kinds that live in the US and in ponds.

Only the water-net caddis fly live in swift moving streams. They build a net or case in the shape of a funnel.  The wide end of the net points upstream and the narrow end downstream. At the narrow end it builds a silk den that the fly cements tiny pebbles where larva lives in the den and eats other tiny animals that come downstream.

(Test or quiz essay question) How does a caddisfly in swift moving streams build a nest?) 

(Write on blackboard-terms - ecology and ecologists and define.)

Ecology- the study of organisms in their various environments and how they adapt to their changing societies.

Ecologists- the scientists who do investigations in the various organisms environments and to investigate the interdependence of the organisms in their and other environments.

The text mentions a question (Why would ecologists study pollution of the water, air or land?)

Adaptation is also a way to show how water life can change or not; by appearances and surroundings.

Plants in Mountain Streams

The plants root themselves firmly into the gravel bottoms.  Found only at the edges or in pools of relatively quiet water.  (Write on Blackboard and in their notebooks- term- alga- Cladophora- lives both in ponds and mountain streams. They have structures to attach themselves to the bottoms of streams, even in swiftly flowing water.  Streams have limited plant life over ponds.

Interdependence in Communities

Animal life usually follows a food chain follows a food chain with bigger animals eating smaller animals.  As plants and animals die they decay (define ‘decay’) the complex substances of the body are changed by bacteria into simpler substances that are used again by green plants to manufacture food.

                                Plants make food

                                Small animals eat plants

                                Larger animals eat smaller animals

                                     And so and so on.


Life in Deep Lakes

Ponds and lakes fed by streams or springs.    Water in ponds and lakes are stagnant.

Ponds are shallow and lakes are deep.

Differences in water temperature from top to bottom.

‘Climates in a Lake’

        Contractions and Expansions

            Heavier               lighter

            Sinks                   rises

        (Draw this chart on blackboard)

Surface is warmer than the bottom of ponds and lakes. 

Define and write the term ‘food chain’ on blackboard-  One kind of organism provides food for a second organism, the second organism provides for a third organism, and so on and on.  Bigger eats smaller.

(Write the term ‘link’ and define on blackboard- to designate the living organisms that occupy a certain ‘niche’ that play a certain role in relation to the other organisms.  There is more food on the top of lakes and ponds due to the sunlight that is present - affecting the temperature and food growth. 

In dealing with water temperature there is a considerable difference in temperature at different levels in a deep lake. 

Other differences

   Winds blow on the surface of water into waves.

   Motion of waves and winds raises air into the water.

   Waves cause the waters itself to mix down to a depth of nine meters or so.  Lower than this no or little mixing of the water so deeper water is quiet water.

Life at the Bottom

   The textbook asks the question “Would you expect to find life at the bottom of a deep lake?”  How and when do you think that animals in the lake survive? When the upper plant bodies die they sink to the bottom slowly and come to rest on the bottom.  There are tiny plant-eating animals and ‘eat’ the falling ‘rain’ of green plants either while they are drifting down or after they reach the bottom.

Animals that live on the surface, die, sink, and could also be eaten by larger animals.  In the deeper levels of the lake the meat-eating lake fish hunt and eat living fish and other animals that eat the dead animals. 

Seasons in a Lake

Autumn-  colder air,  water cools, contracts, becomes heavier, cooler and heavier water sinks. Weather begins getting colder- surface water continues to cool and sink.  This cooling and sinking is like a giant spoon that mixes the water thoroughly as this continues ‘ice’ begins to form.

Winter- the coldest water would settle to the bottom where it would freeze and this would be bad.

What really happens?  Water cools to 4 degrees Celius, sinks to the bottom, warm water from below rises up to the surface, cooled to 4 degrees Celius, and keeps continuing till lake temperature is the same.  Ice begins to form as weather and air gets colder ice becomes thicker, even though ice is only on surface there is still unfrozen water even in the very cold and long winter.

Spring and Summer- more life is abundant and active near the surface of the lake.

Winter time the lake is covered in ice and prevents air from mixing with the water.  Results in less dissolved oxygen in the winter water.  The snow and ice also protect the water from the cold winter air.  Changes in air temperature have less effect on water temperature below the ice covering.  Because the temperature of the water in winter remains fairly constant vertical movement of the water is limited.

     Very important-the sheet of surface ice does not let light pass through it as easily as liquid water does.  Less light in winter than in summer, when a layer of snow covers the ice there is very little light that penetrates to the water below.

  (Teachers if possible to still use or get this text the diagrams on pp. 18-19 show table.)

Result of environmental changes in winter is that life in a lake goes at a slower pace.


Respiration          all activities         moves more slowly in winter

Only a few reproduce themselves- Plants manufacture less food- animals are sluggish as well in winter than in Summer.

(Teacher can ask students “How do you feel in the Winter and Summer?”  “Do you see any similarities? 

New term to write in notebooks and blackboard-  define ‘hibernate’-the body chemistry slows down until it almost ceases entirely- a deep sleep while buried in mud or sand or the bottom of the lake.  Survives on fat reserves of the body.


The sun’s radiation finally melts the ice; surface water is warmer again; temperature it is slightly heavier and warmer than the water below the surface.

Surface water sinks and deeper cooler and lighter water below it rises.  This starts the mixing of the water again till about 14 meters mixed with air from the surface.

Algae is starting to manufacture more food and reproduces themselves again as they are swept down and up with the currents of the sinking and rising waters.

   Water animals having eaten little in winter start to become more active.

(Teacher- Ask the students if they do accept this statement the book suggests.)  (The ecology of an environment must be maintained if the plants and animals in it are to survive? Why?)

All living things are dependent on one another and in their environments.

What is a concept?  Helps to organize our thoughts about various aspects in our universe.

Terms to review:  adaptation, interdependence, community, concept, ecology, ecologist, hibernate, larvae

End of Chapter One

Next Lecture

Learning about how to use the microscope

Written by Mark Graham, Education World® Contributing Writer

Mark has earned two Bachelor degrees, a Master's, a Post-master's and Doctorate in Education, College teaching, Curriculum and instruction, Reading and literacy as well as a certificate in Children's literature.