Unit 3: Life on Earth

• What is biodiversity?


  Biodiversity is the number and variety of organisms found within a specified geographic region.
• What is the term for the area in which an organism lives?

  The area in which an organism lives is called its habitat.
• How is a population defined in ecology?

  A population is made up of all the organisms of one kind (species) in a specific area.
• What constitutes an ecosystem?

  An ecosystem consists of all the organisms (the community) living in a particular area and the non-living components with which the organisms interact.
• What is a niche in an ecological context?

  A niche is the role that an organism plays within a community, including its resource use and interactions with other organisms.
• What are biotic factors in an ecosystem?

  Biotic factors are factors related to living things, such as competition, food availability, and predation.
• What are abiotic factors in an ecosystem?

  Abiotic factors are non-living factors, such as moisture level, pH, light intensity, and temperature.
• How do human influences affect ecosystems?

  Human influences can lead to pollution, habitat destruction, desertification, and the endangerment of species.
• What are producers in an ecosystem?

  Producers are organisms that make their own food, such as green plants.
• What process do green plants use to make their own food?

  Green plants make their own food using light energy from the sun in a process called photosynthesis.
• What is the term for organisms that obtain food by feeding on other organisms?

  These organisms are called consumers.
• What is a food chain?

  The feeding relationship between organisms is called a food chain.
• What do the arrows in a food chain represent?

  The arrows in a food chain point from the food source to the feeder, showing the direction of energy flow.
• What is a food web?

  The interconnection of many food chains is called a food web.
• What type of energy is transferred at each stage in a food chain or web?

  The type of energy transferred at each stage is chemical energy.
• What happens to energy at each stage in a food chain or web?

  At each stage, some energy is lost in heat production, waste, or movement.
• What trend is observed in the number of organisms as you move along a food chain?

  In general, as you move along a food chain from producers through consumers, the number of organisms decreases.
• What is a pyramid of numbers?

  A pyramid of numbers represents the number of organisms at each trophic level in a food chain.
• What is a pyramid of energy?

  A pyramid of energy shows the relative quantity of energy (kJ/m²/year) at each stage in a food chain.
• How does biomass and energy change as you move along a food chain?

  Biomass and energy always decrease as you move along a food chain because energy is lost at each step.
• What resources do organisms compete for in ecosystems?

  Organisms compete for resources such as food, minerals, water, and light.
• What is interspecific competition?

  Interspecific competition occurs when individuals of different species compete for similar resources in an ecosystem.
• What is intraspecific competition?

  Intraspecific competition occurs when individuals of the same species compete for exactly the same resources.
• Why is intraspecific competition more intense than interspecific competition?

  Intraspecific competition is more intense because individuals of the same species compete for identical resources.
• How can the number of plants and animals in an ecosystem be estimated?

  The number can be estimated by counting a sample and taking many samples for reliability.
• What is a quadrat used for?

  A quadrat is used to sample stationary animals or plants by marking a region of known square area.
• What does the term abundance refer to in a quadrat?

  Abundance refers to the number of small squares containing one or more organisms in a quadrat.
• How can the validity and reliability of quadrat sampling be ensured?

  Quadrats should be placed randomly, all organisms counted, and placed as frequently as possible.
• How can small soil animals be sampled?

  Small soil animals can be sampled using a pitfall trap.
• What are the requirements for placing pitfall traps?

  Pitfall traps should be placed randomly, level with the ground, and covered without preventing small organisms from entering.
• How can abiotic factors be measured?

  Abiotic factors can be measured using appropriate electronic instruments for light intensity, temperature, pH, and soil moisture.
• What precautions should be taken when determining abiotic factors?

  Readings should be taken consistently, and many readings should be averaged for valid results.
• What can control the distribution of organisms in an ecosystem?

  The distribution of organisms may be controlled by various abiotic factors.
• How can the effect of an abiotic factor on the distribution of organisms be investigated?

  Samples are usually taken along a line called a transect to relate the presence of a plant species to an abiotic factor.
• What are indicator species?

  Indicator species are species that indicate environmental quality or levels of pollution.
• How can freshwater invertebrates and lichens be used in environmental assessment?

  Freshwater invertebrates can assess freshwater quality, while lichens can indicate local air quality.
• What is the process by which green plants produce their own food?

  The process is called photosynthesis.
• What do green plants absorb during photosynthesis?

  Green plants absorb light energy and convert it into chemical energy in the form of sugar and starch.
• How can the presence of starch in a leaf be demonstrated?

  By boiling the leaf in water, decolourising it in boiling alcohol, and staining it with iodine solution.
• What happens to starch when a plant is placed in the dark for 48 hours?

  The starch present is broken down into sugar and used in respiration.