Lesson Overview 8.2 Photosynthesis:

An Overview

Pigments

Plants gather the sun’s energy with light-absorbing molecules

called pigments.

The plants’ principal pigment is chlorophyll.

Pigments

The two types of chlorophyll found in plants, chlorophyll a and

chlorophyll b, absorb light very well in the blue-violet and red regions of

the visible spectrum, but not in the green region, as shown in the graph.

Leaves reflect green light, which is why plants look green.

Lesson Overview Leaves

Gas Exchange

Leaves take in carbon dioxide and give off oxygen during photosynthesis. When plant cells use the food they make, the cells respire, taking in oxygen and giving off carbon dioxide. Plant leaves allow gas exchange between air spaces in the spongy mesophyll and the exterior by opening their stomata.

Homeostasis

If stomata were kept open all the time, water loss due to transpiration would be so great that few plants would be able to take in enough water to survive. Plants maintain homeostasis by keeping their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water.

Homeostasis

Guard cells, shown in the figure, are highly specialized cells that surround the stomata and control their opening and closing. Guard cells regulate the movement of gases into and out of leaf tissues.

Homeostasis

Carbon dioxide can enter through the open stomata, and water is lost by transpiration.

Homeostasis

When water is abundant, it flows into the leaf, raising water pressure in the guard cells, which opens the stomata. The thin outer walls of the guard cells are forced into a curved shape, which pulls the thick inner walls away from one another, opening the stoma.

Homeostasis

When water is scarce, water pressure within the guard cells decreases, the inner walls pull together, and the stoma closes. This reduces further water loss by limiting transpiration.

Homeostasis

In general, stomata are open during the daytime, when photosynthesis is active, and closed at night, when open stomata would only lead to water loss. However, stomata may be closed even in bright sunlight under hot, dry conditions in which water conservation is a matter of life and death. Guard cells respond to conditions in the environment, such as wind and temperature, helping to maintain homeostasis within a leaf.

Chloroplasts

Photosynthesis takes place inside organelles called chloroplasts.

Chloroplasts contain saclike photosynthetic membranes called

thylakoids, which are interconnected and arranged in stacks known as

grana.

Chloroplasts

Pigments are located in the thylakoid membranes.

The fluid portion outside of the thylakoids is known as the stroma.

An Overview of Photosynthesis

Photosynthesis uses the energy of sunlight to convert water and carbon

dioxide into high-energy sugars and oxygen.

In symbols:

6 CO2 + 6 H2O C6H12O6 + 6 O2

In words:

Carbon dioxide + Water Sugars + Oxygen

An Overview of Photosynthesis

Plants use the sugars generated

by photosynthesis to produce

complex carbohydrates such as

starches, and to provide energy

for the synthesis of other

compounds, including proteins

and lipids.

Cell Respiration Background

1.QUESTION: WHAT TWO ORGANELLES ARE INVOLVED IN

CAPTURING AND RELEASING ENERGY (you should know from

Cell Organelle notes)

a. Chloroplast (Capture energy/in plants)

b. Mitochondria (Release energy/in plants & animals)

2.Cellular respiration is the process that releases energy from food

in the presence of oxygen.

3.Energy stored in food expressed in calories = amount of energy

needed to raise the temperature of 1g of H2O by 1°C.

4.Requires oxygen

5. Chemical equation:

6 O2 + C6H12O6 6 CO2 + 6 H2O + Energy

*Does this look familiar????

6. Photosynthesis removes CO2 from the atmosphere, and cellular

respiration puts it back

7. Photosynthesis releases O2 into the atmosphere, and cellular

respiration uses that O2 to release energy from food

Comparing Photosynthesis & Cellular Respiration

1. Photosynthesis and cellular respiration are opposite processes.

2. The energy flows in opposite directions. Photosynthesis “deposits” energy, and cellular respiration “withdraws” energy.

3. The reactants of cellular respiration are the products of photosynthesis and vice versa.

4. Photosynthesis occurs in the chloroplast (thylakoid and stroma). Cellular respiration occurs in the cytoplasm and mitochondria.