B2b Flashcards
What does the term trophic level mean?
A trophic level is a feeding level. The amount of energy, biomass and usually the number of organisms all decrease as you move up a trophic level.
What is a producer?
Producers can capture their own energy , by photosynthesis. There are other organisms other than green plants that are producers.
Why are some organisms both primary and secondary consumers?
Primary consumer - herbivores, eat plant material, and are the first consumer.
Secondary consumer - carnivores, eat animal materials, and ae the next consumer.
Some organisms can be both primary and secondary consumers because they eat both plants and animals, they are omnivores.
How may changes in the population of one organism affect the other organisms in a food web?
If one organism population increases or decreases it can affect other organisms in the food web. Some animals can just eat more of another organism, if food is in short supply, but others may starve and die.
How do pyramids of biomass show the dry mass of living material?
Each bar on a pyramid of biomass shows the mass of living material at that stage of the food chain - basically how much all the organisms at each level would weigh if you put them all together.
What information would you be given when constructing a pyramid of biomass?
The dry biomass at each level.
Why are the pyramids of numbers and the pyramids of biomass for the same food chains different shapes?
Biomass pyramids are always pyramid shaped because biomass is lost at each stage in the food chain. So the longest bar would be at the bottom and the bars would get shorter at each level going up. Whereas, each bar on a pyramid of numbers shows the number of organisms at that stage of the food chain - not the mass. Therefore pyramids of numbers can be other shapes with each bar being a random length depending on how many of each organism there is.
What are the difficulties in constructing pyramids of biomass?
Organisms may belong to more than one trophic level, for example an organism may feed on two instead of one type of organism.
Measuring dry biomass can be difficult though because you have to kill the organisms to work it out. It would be unethical to kill lots of animals every time you wanted to make a pyramid of biomass.
How does energy from the sun flow through food chains?
The arrows in a food chain represent the flow of energy. Energy from the sun is the source of energy for nearly all life on earth. Plants use a small percentage of the light energy from the sun to make food during photosynthesis. This energy then works its way through the food chain as animals eat the plants and each other.
How is some energy transferred to less useful forms at each stage in the food chain?
The energy lost at each stage is used for staying alive, i.e. in respiration, which powers all life processes. Most of this energy is eventually lost as heat to the surroundings. Material and energy are also lost from the food chain as waste products. Egestion is when food that can’t be digested passes out as faeces. Excretion is when the waste products of bodily products are released e.g. urine.
How can excretory products, faeces and uneaten parts be used as the starting point for other food chains?
Waste products and uneaten parts (e.g. bones) can become starting points for other food chains. For example, houseflies love to eat faeces.
How does the efficiency of energy transfer explain the shape of pyramids of biomass?
Material and energy are both lost at each stage of the food chain. This explains why you get pyramids of biomass. Most of the biomass is lost and so does not become biomass in the next level.
How does the efficiency of energy transfer explain the limited length of food chains?
So much energy is lost at each stage that there’s not enough left to support more organisms after four or five trophic levels.
How do you work out how much energy has been lost at each stage in a food chain?
The numbers show the amount of energy available to the next level. So the first number is how much is available to the next stage and so on.
You can work out how much energy has been lost at each level by taking away the energy that is available to the next level from the energy that was available from the previous level.
How do you calculate the efficiency of energy transfer?
efficiency = energy available to the next level/ energy that was available to the previous level (x200)
