Chapter 2 Plant Structures and Functions
Lesson 3 Photosynthesis and Respiration
Main Idea
Plants use carbon dioxide and sunlight to build sugar and release oxygen.
Plants and animals break down sugar to release energy, carbon dioxide, and
water.
Vocabulary
Photosynthesis (92) – process in a plant whereby the plant takes in carbon
dioxide, water, and the sun’s energy and produces sugar.
Stomata (92) – tiny plant pores that enable carbon dioxide to enter a plant
Carbohydrate (94) – a group of substances made from carbon, hydrogen,
and oxygen.
Cellular respiration (95) – process by plants and animals use oxygen to break
down carbohydrates.
2.3.1 What do leaves do?
Main Idea
Leaves capture and use the energy of the sun to make food through
photosynthesis.
Supporting Details
A. A plant’s food is made in their leaves using the photosynthesis
process. It uses
a. Energy captured from the sun’s rays
b. Carbon dioxide absorbed from the air
c. Water absorbed from the ground or the air
B. Sun’s energy
a. Chloroplast organelles contain a green chemical called
chlorophyll
b. Chlorophyll absorbs and traps the energy from sunlight.
C. Carbon dioxide
a. A plant absorbs carbon dioxide from the air.
b. The carbon dioxide enters a plant through the stomata
i. Stomata are tiny pores found on the bottom of leaves
ii. The pores open and close
1. to absorb carbon dioxide, a reactant for
photosynthesis
2. to release oxygen, a product from photosynthesis
3. to give off excess water vapors
c. Two guard cells surround the stomata.
i. The cells open and close the stomata in response to the
amount of water and light a plant needs.
ii. When the plant needs water, the cells close the stomata
to save water from being released
D. Water
a. Water is transported to the chloroplast from the xylem in the
leaf.
b. It is connected to the xylem in the stem
E. Photosynthesis process
a. Photosynthesis takes place in the chloroplast organelle located
underneath the epidermis (outer most layer of a leaf).
b. Water and carbon dioxide
i. enter the chloroplast
ii. combine using the sun’s energy
iii. producing sugar and oxygen from the reaction
c. Sugar is transported through the phloem in the leaves to the
phloem in the stem for use throughout the plant.
d. Oxygen is released in the air through the stomata.
F. Chemical formula for photosynthesis
Sun’s energy + 6CO2 + 6H2O → C6H12O6 + 6O2
2.3.2 What is the photosynthesis and respiration cycle?
Main Idea
Photosynthesis uses light energy, carbon dioxide, and water to produce sugar
and oxygen. Sugar is used for food in plants.
Supporting Details
A. Photosynthesis and respiration process provide energy to plants and
animals.
B. The sugar, produced by plants, is a carbohydrate.
a. Carbohydrate is a group of substances.
b. It consists of carbon, hydrogen, and oxygen.
C. Carbohydrates can be modified to make structural materials.
a. Carbohydrates can be converted into cellulose
b. A plant’s cell walls are made from cellulose
D. Carbohydrates can be stored as food.
a. Plants store sugar as a starch.
E. Starch and cellulose are complex carbohydrates – made up of
thousands of simple sugar units.
F. When animals eat parts of plants, they take in the carbohydrate stored
in that part.
G. When an animal eats parts of another animal, it takes in the
carbohydrate that the animal took from the plant it ate.
H. Plants and animals need the oxygen that plants release during the
photosynthesis process.
a. Oxygen breaks down the stored carbohydrate to get the energy
needed by the plant or animal.
b. The process to break down carbohydrates with oxygen is called
cellular respiration.
2.3.3 Where does respiration happen?
Main Idea
Cellular respiration takes place in the mitochondria.
Supporting Details
A. Cellular respiration occurs in the mitochondria.
B. Mitochondria provide plant and animal cells the energy needed to
function, grow, and repair themselves.
C. A typical cell holds about 1,000 mitochondria.
D. Cellular Respiration process
a. Oxygen and sugar enter the cell and go into the mitochondria
b. The mitochondria uses oxygen to break down the stored
carbohydrate to release energy.
c. Carbon dioxide and water are also released as products of the
chemical reaction
d. The mitochondria changes the released energy into a substance
called ATP.
i. ATP is the cell’s energy battery.
ii. The batteries are in constant use.
E. Chemical formula for cellular respiration
C6H12O6 + 6O2 → energy + 6CO2 + 6H2O