Student “Need to Know” for Energy Transfer (Photosynthesis & Cell Respiration)

WATCH THIS VIDEO ON Energy Transfer: https://www.youtube.com/watch?v=lnAKICtJIA4

The processes of photosynthesis and cell respiration are interdependent and move energy through ecosystems.

The products of photosynthesis (oxygen and sugar) are the reactants of cell respiration.

The products of cell respiration (carbon dioxide and water) are the reactants of photosynthesis.

The energy in most ecosystems flows through the food web. The energy flow starts in green plants that harvest some of the sun’s energy using photosynthesis. The plants are then consumed by animals, bacteria and other creatures, which are themselves eaten by other creatures. These animals eat so that they can use the sugars from food during cellular respiration – to produce ATP.

Autotrophs are organisms that can capture energy from sunlight and use it to produce its own food. Because they make their own food, autotrophs are also called producers.

Heterotrophs are organisms that rely on other organisms for their energy and food supply (must EAT). Because they must eat to get energy, heterotrophs are also called consumers.

Energy flows through an ecosystem IN ONE DIRECTION, from the sun to autotrophs (producers) and then to various heterotrophs (consumers).

• The energy stored by producers can be passed through an ecosystem along food chains and food webs.• A food chain is a series of steps in which organisms transfer energy by eating and being eaten.• A food web links all of the food chains in an ecosystem together.

Each step in a food chain or web is called a trophic level (trophic means “food or nourishment”).

• Producers make up 1st trophic level – photosynthesis occurs here.• Consumers make up secondary, tertiary, and higher trophic levels –

cell respiration occurs here.• Each consumer depends on the trophic level below for energy.• Energy flows in one direction only!• Only about 10% of the energy available within 1 trophic level is

transferred to organisms at the next trophic level – the rest is used up or lost as heat.

Photosynthesis is the process whereby light energy is used to build sugar in the chloroplasts of plant cells. In the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen.

• 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2

• carbon dioxide + water + light → sugar + oxygen

Animals eat other organisms for food, but food is not a direct source of energy for cells. Instead, all organisms break down molecules from food to produce ATP. Because it occurs in the presence of oxygen, cellular respiration is known as aerobic respiration – it occurs in the mitochondria of plant and animal cells – ALL LIVING THINGS RESPIRE.

• 6O2 + C6H12O6 → 6 CO2 + 6 H2O + Energy• oxygen + glucose → carbon dioxide + water + ATP

WATCH THIS VIDEO ON THE CARBON CYCLE: https://www.youtube.com/watch?v=nzImo8kSXiU

Energy flows through ecosystems in ONE DIRECTION ONLY, but matter, such as carbon is RECYCLED.

Biogeochemical cycles pass the same molecules around again and again within the biosphere.

Nutrients are the body’s building blocks. Every living organism needs nutrients to grow and carry out essential life functions. Nutrients are passed between organisms and the environment through biogeochemical cycles.

Because nutrients are in short supply in many ecosystems, recycling of nutrients is essential for these ecosystems to keep functioning.

The Carbon Cycle

Carbon is the key ingredient in all living organisms. Carbon is also found in oceans, the air, and certain types of rock.

• The 4 kinds of processes involved in the carbon cycle are:1. Biological (photosynthesis, respiration, decomposition)2. Geochemical (release of CO2 into atmosphere by volcanos)3. Mixed biogeochemical (burial of carbon remains and their conversion into coal & petroleum (fossil fuels)

by the pressure of overlying earth)4. Human activity (mining, burning of fossil fuels and cutting & burning of forests)

• In the atmosphere, carbon is present as CO2 gas. • CO2 is released into the atmosphere by volcanic activity, respiration, human activities such as burning fossil

fuels, and the decomposition of organic matter.• Plants take in CO2 during photosynthesis. They use the CO2 to build carbohydrates which are then passed along

food webs to consumers. This is VERY important because photosynthesis is one of the few processes that REMOVES excess carbon from the atmosphere.

The Role of Photosynthesis & Cell Respiration in the Carbon Cycle

• Cellular respiration and photosynthesis are important parts of the carbon cycle. • The carbon cycle is the pathways through which carbon is recycled in the biosphere. • While cellular respiration releases carbon dioxide into the environment, photosynthesis pulls carbon dioxide out

of the atmosphere. • The exchange of carbon dioxide and oxygen during photosynthesis and cellular respiration worldwide helps to

keep atmospheric oxygen and carbon dioxide at stable levels.