Biological Diversity

By the end of this unit you can:

Define a habitat as the place and conditions in which an organism lives.
Describe what a producer is in an ecosystem, and why ecosystems cannot exist without them.
Describe the process of photosynthesis in terms of chlorophyll, carbon dioxide, water and glucose.
Investigate the relationship between sunlight and the presence of starch in leaves.
Investigate the relationship between the amount of light and the amount of oxygen produced in plants.
Describe the process of respiration in terms of glucose, oxygen, energy, carbon dioxide, and water.
·Construct a simple food chain.
Construct a simple food web.
Be able to identify primary, secondary and tertiary consumers on a food web.
Discuss the relationships between organisms on a food web and predict changes that could occur due to an increase or decrease in the population of one organism.
Be able to explain that there is a 10% energy loss when energy flows along a food chain.
Describe and identify abiotic and biotic factors that affect the population size.
Understand the importance of decomposers in a community/ food web and be able to discuss why decomposers are essential to the continuation of life on Earth.
Investigate the factors that affect decomposition.
Discuss the importance of biodiversity.
Be able to carry out fair sampling using quadrat frames and transect lines.
Be able to strip Harakeke to expose and weave the fibres.

This unit is about an area of biology called ecology. Ecology looks at the ways that living things interact with each other and the environment around them. Changes in the environment or changes in the organisms can cause big changes to the living community, which can result in a new balance being found across it.

A community of living things in a place is sometimes called an ecosystem. We will begin by looking at food chains. These are a simple way of analyzing the flow of energy through an ecosystem. At the bottom of all food chains are organisms which produce their own food from raw ingredients and energy. These organisms are called producers.

Most of the producers we are familiar with use the Sun as their energy source. Some or the organisms in the deep sea, or deep underground, use chemical energy from rocks as an energy source. These producers are common but relatively unknown because they live in places that humans don't go often.

Producers

All producers make their own food molecules from an external energy source. There are two ways of doing this:

using the energy released in chemical reactions (chemosynthesis)
using the energy of sunlight (photosynthesis).

The first life forms on Earth were chemosynthetic. This is less efficient than using light, so when photosynthetic life evolved the chemosynthetic organisms were banished to places where light is not available, such as deep-sea hydrothermal vents or deep in the rock of Earth's crust. All chemosynthetic organisms belong to the prokaryotes (bacteria and relatied things).

Photosynthetic organisms capture the energy of the sunlight using a special pigment called Chlorophyll. This pigment gives plants their green colour. Because Photosynthesis is more efficient than Chemosynthesis it can be used to power both unicellular (algea and bacteria) and multicellular organisms (plants). It also produces oxygen which most of the living world needs to survive and produce energy.

Photosynthesis

As we already know photosynthesis is a process that plants, algae, and some bacteria use to create food molecules using light. What else does it need though?

Photosynthesis uses carbon dioxide from the atmosphere and water from the ground. When sunlight is present plants can convert these two things into glucose (the simplest sugar) and oxygen. Plants don't normally store the food as glucose because this would cause problems for them (like it does in diabetics). Instead they join the glucose molecules together to make starch. Some of this is stored in the leaves, but many plants have specialised structures for starch storage e.g. tubers (potato, taro, kumara).

If you have time watch this video about the history of photosynthesis. It took scientists many years to discover the reason behind plants growth. Some of the simple experiments they take you through in this video are:

Plant a tree in a bucket with an amount of dry soil that you know the mass of. Water the tree and after a few years of watering the tree every few days weigh the soil and tree again. The mass of the tree has grown but the dry mass of the soil has not changed. This experiment was done in the 1600's by a Scientist called Van Helmont. He concluded that the tree grew not from the dirt but from the water in the bucket.
Wrap part of a leaf in foil/paper to block the sunlight. Leave it in light for a while and then use iodine to test the leaf for starch. The part of the leaf covered by the foil will test negative for starch while the rest of the leaf will test positive. This experiment was the first to show light was essential for plant growth.
Cover a leaf in petroleum gel and put it in the sunlight. The petroleum gel is transparent so light still its absorbed by the leaf. However, the gel stops carbon dioxide from entering the leaf. Test the covered leaf against another leaf from the same plant and you will see the covered leaf has produced no starch while the normal leaf has produced starch.

Checkpoint

Producers are organisms that make their own food.
Producers make their food by a process called photosynthesis.
Photosynthesis is a chemical reaction where plants react (only in the presence of light) carbon dioxide and water to produce sugar (glucose) and oxygen.
Plants store this sugar in long chains of sugar called starch.
Photosynthesis occurs in a cell structure called a chloroplast which contains a special green pigment called chlorophyll which allows sunlight to be captured and used.

Take the quiz found here to see how much you know!

Food Chains and Food Webs

Food chains are a simple way of showing how energy flows from one organism to another in an ecosystem. Iowa produces the most corn (maize) out of any state in America. Locusts are a common pest to corn farmers as they can decimate crops. Lizards eat locusts and other insects but get eaten by snakes. A simple food chain of the flow of energy in this example would show the energy starting off with the corn as it is the only organism that produces its own food. The locusts rely on the corn for their energy and so eat the corn to gain energy. Lizards then eat the locusts and gain some of the energy that the locusts gained from the corn. Snakes then eat the lizards and gain some of the energy that the lizard gained from the locusts.

As you can see all the original energy comes from the corn. Energy is spent by the locusts moving and reproducing and so less energy is available for the lizards. The lizards also move and reproduce and so even less energy is left for the snakes. As a guide line only about 10% of the energy is passed onto the next organism in the food chain. This means that the locusts get 10% of the energy of the corn. The lizards gain 10% of the locusts energy when they consume them. The snakes receive 10% of the energy that the lizards gained from the locusts which is only 0.1% of the energy the locusts received from the corn.

This rule of 10% severally limits the amount of organisms found in food chains. Since only 10% of the energy is passed along each time the fifth organism in a chain receives 1/10000th of the energy. Because of this food chains are normally 4-5 organisms long and rarely go past this.

In this food chain the corn is the producer of all the energy that enters the system. Since the locusts consume the corn they are what we term a primary (first order) consumer. The lizards consume the locusts and so are a secondary (second order) consumer with the snakes being the tertiary (third order) consumer and if nothing consumes the snakes we also term them the apex (top) predator.

Checkpoint

Food chains show how energy flows from one organism to another. This is what the arrows show in a food chain.
Food chains always start with a producer. The organism that gets energy by eating producers is a primary consumer. The organism that gets energy by eating primary consumers is called a secondary consumer.
About 10% of the energy from each level is transferred to the next. This limits how many steps a food chain can contain.

If you are confident take this quiz to find out if you know it all!

Food Webs

A food chain is a very simplistic view of the energy flow. A real ecosystem has multiple different organisms all of which might interact differently. There are normally multiple producers and consumers in every ecosystem.

In a food web producers are shown at the bottom. As you go up the food web you also go up trophic levels. A food web shows multiple food chains from one ecosystem. From the food web shown you could have food chains such as

Corn ⇾ Grasshopper ⇾ Rat ⇾ Wolf ⇾ Python ⇾ Eagle

Mangoes ⇾ Fruitfly ⇾ Dragonfly ⇾ Thrust ⇾ Eagle

Food webs are more useful as they help us analyse the wider impacts of changes that could affect the ecosystem. If a farmer placed rat poison which killed off most of the rats the grasshopper population would increase as one of its major predators is gone. These grasshoppers would eat more corn and so the amount of corn would be reduced. The frogs population could increase due to more prey for them to eat. Without rats to eat some pythons could starve. The impacts of changes in ecosystems are extensive and sometimes hard to predict.

Some species are what we term keystone species. Without this species the whole ecosystem would collapse and change forever. This video might help you understand keystone species in more detail.

Checkpoint

Food webs so the many different food chains in an ecosystem. This is better as it shows us more clearly how organisms depend and interact with each other.
If an event happens which affects just one species in the food web, the affect will flow on to all nearly all the organisms in the food web. We focus on the most immediately impacted organisms. e.g. the organisms that are get eaten by the species affected or the organisms that eat the species affected.
An apex predator is an organism that is at the top of its food web. No organisms eat it.
All energy in any ecosystem always starts with a producer.

Test your knowledge on food webs using this quiz.

Decomposers and Scavengers

Two groups of organisms that the food web doesn't show are scavengers and decomposers.

Scavengers are organisms which eat dead things, They are important because their waste is easier to break down than the dead organisms themselves. Without them, dead material would build up because it break down very slowly.

A second, and even more important group, is decomposers. The difference between scavengers and decomposers is that scavengers digestive inside of their bodies in the same way as other animals.

Decomposers carry out extracellular digestion. They release enzymes, chemicals which cause the food molecules (polysaccharides, proteins, lipids) into simpler molecules (amino acids, simple sugars, fatty acids) which can be directly absorbed through the cell membranes. Decomposers include bacteria and fungi.

Decomposers are very important because they often convert molecules containing nitrogen into a form that plants can use as a nutrient.

For example, plants cannot directly use the nitrogen in urine - a chemical called urea. However, to bacteria urea is a food. When they eat it, they convert it to ammonia and nitrate (this is why an unwashed urinal smells of ammonia). Both of these forms of nitrogen can be taken up by plants (which must have nitrogen from their roots to grow)

Checkpoint

Decomposers breakdown dead organisms by a process called extracellular digestion
This involves the decomposer releasing enzymes which break down the dead tissue into small molecules for them to be absorbed.
This is very important as without decomposers dead tissue would not be recycled and reintroduced into the ecosystem.

Checkout your knowledge of decomposers with this quiz!

Rotting_Watermelon_Decomposition_Timelapse_Footage.mp4

Checkpoint

Decomposers breakdown dead organisms by a process called extracellular digestion
This involves the decomposer releasing enzymes which break down the dead tissue into small molecules for them to be absorbed.
This is very important as without decomposers dead tissue would not be recycled and reintroduced into the ecosystem.

Checkout your knowledge of decomposers with this quiz!

Specific Learning Outcomes

By the end of this unit you can:

Define a habitat as the place and conditions in which an organism lives.
Describe what a producer is in an ecosystem, and why ecosystems cannot exist without them.
Describe the process of photosynthesis in terms of chlorophyll, carbon dioxide, water and glucose.
Investigate the relationship between sunlight and the presence of starch in leaves.
Investigate the relationship between the amount of light and the amount of oxygen produced in plants.
Describe the process of respiration in terms of glucose, oxygen, energy, carbon dioxide, and water.
·Construct a simple food chain.
Construct a simple food web.
Be able to identify primary, secondary and tertiary consumers on a food web.
Discuss the relationships between organisms on a food web and predict changes that could occur due to an increase or decrease in the population of one organism.
Be able to explain that there is a 10% energy loss when energy flows along a food chain.
Describe and identify abiotic and biotic factors that affect the population size.
Understand the importance of decomposers in a community/ food web and be able to discuss why decomposers are essential to the continuation of life on Earth.
Investigate the factors that affect decomposition.
Discuss the importance of biodiversity.
Be able to carry out fair sampling using quadrat frames and transect lines.
Be able to strip Harakeke to expose and weave the fibres.

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