Study an Ecosystem, Grade 10: Quadrats, Soil Tests and Field Readings

A square quadrat frame made of four sticks tied with white string, lying on dry grassland with small yellow flowers

Four practicals for the Grade 10 ecosystem study, covering the biotic and abiotic factors CAPS asks learners to study in one local ecosystem.

Subject Life Sciences
Grade and term Grade 10, Term 3 (Biosphere to ecosystems), with a repeat visit in Term 4
Topic Study an ecosystem: fieldwork
Practicals Quadrat and transect survey, soil tests, soil water-holding capacity, temperature, humidity and light readings
Time Quadrat survey about 1 hour on site. Soil tests about 40 minutes. Water-holding investigation about 30 minutes. Readings about 5 minutes each time
CAPS task CAPS gives the ecosystem fieldwork (Term 3) as an example of the Grade 10 project or assignment. It counts 100 marks, recorded in Term 4.

Practical 1: a plant survey with quadrats and a transect

Aim

To estimate how much of each plant species grows in the study area, and to see how the plants change across it.

What you need

  • A quadrat 1 m × 1 m for each group: four sticks and 4 m of string, or a 0,5 m × 0,5 m frame bent from about 2,2 m of stiff wire (two coat hangers joined)
  • Two long tapes for the grid, at least 20 m each or the length of the study area, such as the 100 m field tape
  • One more tape for the transect, for example a 5 m tape measure
  • Tent pegs or sticks to hold the tapes
  • A field guide or key to local plants
  • A clipboard, results table and pencil
  • A phone or a list of random numbers
  • Hats, sunblock and drinking water

Method

Random quadrats

  1. Lay two tapes along two edges of the study area, at right angles, to make a grid.
  2. Use two random numbers to find a point on the grid, for example 7 m along and 12 m across.
  3. Place the quadrat with one corner on that point.
  4. Write down every plant species inside the quadrat. Call an unknown plant "species A" and photograph it.
  5. Estimate the percentage of the ground each species covers. Count the plants too if they are easy to separate.
  6. Repeat steps 2 to 5 until you have at least 10 quadrats.

Transect

  1. Stretch a tape in a straight line across a change in the area, for example from under a tree into the open.
  2. Place the quadrat beside the tape at 0 m and record the species and percentage cover.
  3. Move the quadrat 1 m along the tape and record again. Carry on to the end of the tape.

What you should see

Diagram comparing random quadrats placed on a grid across a study area with quadrats placed every metre along a transect line

What you work out How What it tells you
Frequency Number of quadrats with the species ÷ total quadrats × 100 How widely the species is spread
Average percentage cover Add the cover for the species in every quadrat and divide by the number of quadrats How much of the ground it takes up
Density Total number of plants ÷ total area sampled, in plants per m² How crowded it is

Along a transect from shade into sun, shade-loving plants drop out and grasses take over.

Why it happens

A study area is too big to count every plant, so you sample small areas and scale up. Random placement stops you choosing the interesting spots, which would bias the result. The average of many quadrats is closer to the truth than one. A transect is used where conditions change across the area, because it shows how the plants change with them.

Safety

  • Work in groups, in sight of the teacher, and get the landowner's permission first.
  • Wear closed shoes. Look before you put your hand into long grass, in case of snakes, scorpions or thorns.
  • Do not taste any plant, and do not touch plants you do not know.
  • Wash your hands before eating and when you get back to school.

Practical 2: soil tests for texture, humus, air content and pH

Aim

To describe the soil at the study site by its texture, humus, air content and pH.

What you need

  • Soil samples from the site, collected in labelled bags, and a garden trowel
  • A clear glass jar with a lid, about 500 ml, such as a jam jar
  • A little dishwashing liquid
  • A small empty tin of about 100 to 150 ml, for example a tomato-paste tin, with the top removed and a few holes punched in its base
  • A 500 ml measuring cylinder and a glass rod or long stick for stirring
  • pH test paper, or red and blue litmus paper
  • A 100 ml plastic beaker and a plastic spatula
  • Distilled water in a wash bottle
  • A ruler and a marker

Method

Texture and humus

  1. Fill the jar one third full of soil. Pick out stones and roots.
  2. Add water until the jar is about three quarters full, and add 2 drops of dishwashing liquid.
  3. Close the lid and shake hard for 2 minutes.
  4. Stand the jar on a level bench and leave it for 24 hours.
  5. Mark the top of each layer on the jar and measure each layer with the ruler.
  6. Rub a pinch of moist soil between your finger and thumb as well, and note how it feels.

Air content

  1. Find the volume of the tin: tape over the holes, fill it with water and pour the water into the measuring cylinder. Remove the tape.
  2. Push the tin, open end down, into undisturbed soil. Dig it out and level the soil with the rim.
  3. Pour 250 ml of water into the measuring cylinder.
  4. Tip all the soil from the tin into the water and stir until no more bubbles rise.
  5. Read the new volume.
  6. Work it out: volume of air = 250 ml + volume of the tin − final volume.

pH

  1. Put 2 spatulas of dry soil in the beaker.
  2. Add the same volume of distilled water and stir for 1 minute. Use distilled water, because tap water has its own pH and would change the reading.
  3. Leave it to settle for 5 minutes.
  4. Dip a pH paper strip into the clear liquid and compare its colour with the chart. With litmus, dip one red and one blue strip.

What you should see

Diagram of a settling jar after 24 hours with sand at the bottom, silt above it, clay on top of the silt, then water, and bits of humus floating on the surface

Test Result What it means
Settling jar Sand at the bottom within a minute, silt above it within hours, clay on top over a day or more. Humus floats The thickest layer shows the main soil type. A good mix of all three is a loam
Feel Gritty, smooth and silky, or sticky Mostly sand, mostly silt, or mostly clay
Air content The final volume is less than 250 ml plus the tin The difference is the air that was between the soil particles
pH paper A colour that matches a number on the chart Below 7 is acidic, 7 is neutral, above 7 is alkaline
Litmus Blue turns red, red turns blue, or neither changes Acidic, alkaline, or close to neutral. Litmus does not change clearly near pH 7, so use pH paper to get a number

Why it happens

Sand grains are the largest and heaviest soil particles, so they sink first. Clay particles are the smallest and stay suspended longest. Humus is decayed plant and animal matter, light enough to float. Water fills the spaces between soil particles and pushes the air out as bubbles.

Safety

  • Soil can carry bacteria and the eggs of parasites. Wash your hands after handling it, and keep it away from your mouth.
  • Mind the sharp edge of the cut tin. Push it in with a flat piece of wood, not your palm.
  • Do not collect soil near rubbish dumps, sewage or broken glass.

Practical 3: how much water different soils hold

Aim

To compare how much water sandy soil, loam and clay soil hold.

What you need

Method

  1. Fold a filter paper into each funnel and wet it with a little water so the paper does not soak up the test water.
  2. Stand each funnel in a measuring cylinder and label them Sand, Loam and Clay. Empty any water that has dripped through.
  3. Measure 50 ml of each dry soil in the beaker, tapping it level, and tip it into its funnel.
  4. Measure 50 ml of water in the fourth cylinder, pour it slowly onto one soil, and start the timer. Do the same for the other two soils.
  5. After 10 minutes, read the volume of water in each cylinder.
  6. Work out the water held: 50 ml − volume collected.
  7. Repeat with fresh soil, or compare with other groups, and work out an average for each soil.

What you should see

Three funnels of sandy soil, loam and clay soil on measuring cylinders, with the most water collected under the sand and the least under the clay

Soil Water that runs through Water held
Sandy soil Most, and fastest Least
Loam Some In between
Clay soil Least, and slowest. It may be cloudy Most

Why it happens

Sand has large particles with large spaces, so water drains through quickly. Clay has tiny particles with tiny spaces, and water clings to their large total surface, so clay holds the most water. Loam holds a useful amount and still drains, which is why it suits most crops.

Variable In this investigation
Independent (what you change) The type of soil
Dependent (what you measure) The volume of water collected after 10 minutes
Controlled (kept the same) Volume of soil, volume of water, time allowed, the same size of funnel and paper, dry soil at the start

Safety

  • Wash your hands after handling soil.
  • Wipe up spilt water and mud so nobody slips.
  • Throw the used soil and filter paper in a bin or outside, not down the sink, where it blocks the drain.

Practical 4: temperature, humidity and light at the site

Aim

To record how air temperature, soil temperature, humidity and light change during the day and between seasons.

What you need

Method

  1. Choose one fixed spot at the site and use it every time.
  2. Hang the air thermometer in the shade about 1,5 m above the ground, because direct sun heats the thermometer itself and gives a reading higher than the air. Wait 3 minutes and read it.
  3. Make a hole 5 cm deep with a pencil or rod. Put the soil thermometer in, firm the soil around it, wait 3 minutes and read it.
  4. Read the humidity from the thermo-hygrometer in the same shade.
  5. Hold the phone flat at the same height, face up, and read the light.
  6. Take readings at the same times each day, for example 08:00, 10:30 and 13:00, for a week. Repeat the week next term to compare the seasons.

What you should see

Reading Early morning Midday
Air temperature Lowest Highest, usually in the early afternoon
Soil temperature at 5 cm Changes less than the air Rises more slowly than the air
Humidity Highest Lowest
Light Low Highest

Draw a line graph of each reading against time, and compare the two terms.

Why it happens

The sun heats the ground and the ground heats the air, so the air is warmest after midday. Soil warms and cools slowly, so the temperature a few centimetres down changes less than the air. Warm air can hold more water vapour, so as the air heats up the relative humidity falls.

Safety

  • A spirit thermometer is glass. If one breaks, do not pick up the pieces with your fingers. Tell the teacher.
  • Do not look directly at the sun when measuring light.

The ecosystem study in brief

CAPS asks each class to study one ecosystem close to the school, within the local biome: vacant land, a park, open veld or the edge of a dam.

What the study must cover

  • The abiotic and biotic factors, and how they affect each other
  • The feeding relationships: who eats whom
  • The biodiversity of the site, identified with field guides and keys
  • Changes between seasons, over two terms: Terms 1 and 2, or Terms 3 and 4
  • Good or bad human impact on the site

Different groups investigate different factors. Each group plans, collects, records and presents, analyses and evaluates its data, and the class then pools the results.

Abiotic factors

Factor What to look at
Physiographic factors Aspect, slope and altitude. In South Africa, north-facing slopes get more sun and are warmer and drier than south-facing slopes
Soil pH, humus content, texture, water-holding capacity and air content
Light Day length and how it changes with the seasons
Temperature The difference between day and night, and between seasons
Water Rainfall and the water cycle. Wetlands store water and filter it
Atmospheric gases and wind Oxygen and carbon dioxide. Wind dries the soil and speeds up water loss from leaves

Biotic factors and feeding relationships

Group What it does Examples you may find
Producers Make food by photosynthesis Grasses, shrubs, trees, algae
Herbivores Eat plants Grasshoppers, caterpillars, snails
Carnivores Eat other animals Spiders, mantids, lizards, birds of prey
Omnivores Eat plants and animals Many ants, some birds
Decomposers Break down dead matter and return nutrients to the soil Fungi, bacteria. Earthworms and millipedes help by breaking up the dead matter

Draw a food chain and a food web from what you find. Collect small animals with a sweep net or a pitfall trap (a cup sunk level with the soil), and return them alive to where you found them.

If your ecosystem is a river or dam

Diagram of mayfly and stonefly nymphs, found in clean water with plenty of oxygen, beside bloodworms and sludge worms, found in water with organic pollution

  • Work from the bank. Collect water in a jar on a stick and test it on dry ground.
  • Bilharzia is caught when the larvae of the parasite, released by freshwater snails, go in through the skin of anyone standing or swimming in infected water. It is found mainly in Limpopo, Mpumalanga and KwaZulu-Natal. Nobody needs to go into the water for this study.
  • Small water animals show how clean the water is. Mayfly and stonefly nymphs need clean, well-oxygenated water. Bloodworms (red midge larvae, which contain haemoglobin) and sludge worms survive where organic pollution has used up the oxygen.

Human impact

Litter, trampled paths, alien plants, overgrazing and dumping harm a site. Clearing alien plants and picking up litter help it recover.

Writing the report

The report has a title, an introduction with the aim, the method, results in tables and graphs, a discussion of what the results mean (including the food web, the seasonal changes and the human impact), a conclusion that answers the aim, and references.

Free worksheet and marking memo

Related practicals

References