2.4: Energy Flow in Ecosystems
pg. 38
Key Concepts:
2. Photosynthesis and cellular respiration are complementary processes in an ecosystem.
Evidence of Learning: Students can …
- explain what happens during both photosynthesis and cellular respiration.
- describe the difference and interdependence between producers and consumers.
- understand that humans depend on plants for both food and oxygen.
Radiant Energy: energy that travels through empty space.
Light Energy: visible forms of radiant energy.
Thermal Energy: the form of energy transferred during heating or cooling.
- A living things require energy to survive (characteristics of living things)
- Energy supplied to our planet comes from the Sun in form of radiant energy, sunlight.
- Sunlight is made up of many different wave lengths of energy known as the light
spectrum.
- visible light is known as white light, there is also Ultra violet light, Inferred light, radio
waves, microwaves, etc.
- 70% of the light is absorbed by hydrosphere and lithosphere, and is converted to
thermal energy, heat.
- 30 % of the energy is reflected back into space.
- 0.23% of the energy is actually absorbed by living things.
- Thermal energy can not be used and is known as waste energy, Light energy is used by
plants for photosynthesis, and is converted to chemical potential energy, glucose.
- Glucose is used by all living organisms to survive. (Cellular Respiration)
Figure 1: The distribution of incoming solar radiation.
Photosynthesis
Photosynthesis: the process in which the Sun’s energy is converted into chemical energy.
Producer: an organism that makes its own energy-rich food components using the Sun’s
energy.
- Plants are organisms that can photosynthesis, use light energy to create chemical
potential energy, in the form of glucose (sugar).
- Plants are known as producers because they can make their own food.
- Plants contain chlorophyll, which make them green in colour, which traps sunlight
energy.
- Cyanobacteria and other algae are found in water, and contain chlorophyll to capture
sunlight for photosynthesis.
Word and Chemical equation for Photosynthesis:
Carbon dioxide + Water → sugar + Oxygen
CO2 + H20 → C6H12O6 + O2
Figure 3: Chemical energy is stored in a variety of plant structures.
- Not all sugars are used for energy, some are structural components used to build cell
walls, or combine with proteins to form other cellular structures.
Figure 4: the molecular structure of a) water, b) carbon dioxide, c) glucose (a sugar), and
d) glutamic acid (a building block of protein).
Cellular Respiration
Cellular Respiration: the process by which sugar and oxygen are converted into carbon
dioxide and water, to provide energy for the cell.
Consumer: an organism that obtains its energy from consuming other organisms.
- All living things must cellular respire, to survive.
- Consumers are organisms that must consume food to obtain energy.
- The chemical potential energy in sugar is released and used by the cell to do work.
Word and Chemical Equations
Oxygen + Sugar → Carbon dioxide + Water
O2 + C6H12O6 → CO2 + H2O
Figure 5: Photosynthesis and cellular respiration are complementary processes.
BLM: 2.4-1: Comparing Photosynthesis and Cellular Respiration
Check Your Learning
Questions 1 – 12, page 41
Summary:
- During photosynthesis, green plants use the Sun’s energy to convert carbon dioxide and
water into sugar (chemical energy) and oxygen.
- During cellular respiration, sugar and oxygen are converted into carbon dioxide, water,
and energy.
- All organisms undergo cellular respiration.
- Producers make their own energy rich food compounds using the Sun’s energy.
- Consumers obtain energy by feeding on other organisms.
- Humans depend on photosynthesizing organisms for food and oxygen.