Photosynthesis-What\'s in a Leaf PDF

Preview

Summary

Download Photosynthesis-What's in a Leaf PDF

Description

Photosynthesis: What’s in a Leaf? What is the relationship between structure and function in a leaf?

Why? What would the world be like without leaves—no grass for ball fields, no beautiful landscaping? It would also mean no oxygen for animals and no food for heterotrophs. Leaves are like living machines that recycle the carbon and oxygen in our environment. This process, driven by the sun’s energy, allows for a constant supply of oxygen and food for the inhabitants of Earth.

Model 1 – Leaf Sun-Catcher Sunlight (energy)

central vein

Water (liquid)

r Suga

s

Water (gas)

Water (gas)

Carbon dioxide

Oxygen

General Equation for Photosynthesis Reactants

Products

light carbon dioxide + water energy ⎯⎯→ sugars + oxygen 1. List three things entering the leaf in Model 1. sunlight, carbon dioxide, water

2. List three substances leaving the leaf. sugars, water (gas), oxygen

3. Which substance is both entering and leaving? water

4. Veins are important structures that carry materials through the leaf. Label the central vein in the leaf diagram. labeled in diagram

Photosynthesis: What’s in a Leaf?

1

5. How is the substance you identified in Question 3 changed between its entry and its exit? Water enters as a liquid and leaves the leaf as a gas.

6. Use the general equation for photosynthesis and Model 1 to answer the following questions. a. What are the reactants for photosynthesis? water, carbon dioxide, and sunlight

b. Where do these reactants enter the leaf? carbon dioxide enters through the underside of the leave; water enters through the central vein; sunlight enters through the top

c. What are the products of photosynthesis? sugars and oxygen

d. From where do the products leave the leaf? oxygen leaves through the central vein; sugars leave through the veins of the leaves

7. Categorize all the components involved in photosynthesis as either matter or energy. carbon dioxide, water, oxygen, and sugar is matter; sunlight is energy

Model 2 – Cross Section of the Internal Structure of a Leaf light energy

Cuticle Upper epidermis Chloroplast Palisade mesophyll sugars leaving leaf

water entering leaf

Vein Air Space

Spongy mesophyll

Lower epidermis

Cuticle Guard cell CO2

Stoma O2

H 2O

8. List the layers of the leaf starting at the upper cuticle all the way to the lower cuticle. cuticle, upper epidermis, palisade mesophyll, vein, spongy mesophyll, lower epidermis, cuticle

2

POGIL™ Activities for High School Biology

Read This! Inside plant veins are two different types of tissues. Xylem carries water and minerals up from the roots of the plant and phloem carries the sugars (nutrients) away from the leaf to areas where the plant is growing or to storage areas in the plant. 9. Describe the position of the vein(s) in each model. a. In the leaf in Model 1. A central vein in the middle and veins branching out throughout the leaf

b. Within the leaf cross section in Model 2. In the middle of the section, positioned in between palisade mesophyll and spongy mesophyll

10. How does the placement of veins help to carry out their function of transporting materials to and from the leaf? Placement gives water easy access to the palisade mesophyll, where photosynthesis takes place.

11. Look back at your answers to Questions 1–3 and the photosynthesis equation. In the appropriate locations on Model 2, mark with labels and arrows what is entering the leaf and what is exiting the leaf. labeled in diagram

12. Which kind(s) of cells have chloroplasts in them? palisade mesophyll and guard cells

13. Remembering the function of chloroplasts, in which part(s) of the leaf is photosynthesis taking place? palisade mesophyll and guard cells, more in the palisade mesophyll

14. The green color of chloroplasts is due to a pigment in them that absorbs light energy. Knowing this, infer which layer inside a leaf gives the whole leaf its green color. Write one complete sentence to express your reasoning. The palisade mesophyll holds densely packed chlorophyll, which makes leaves green.

15. Through which layer(s) does light energy travel to reach the palisade mesophyll? the cuticle and upper epidermis

16. List at least three differences between the cells of the palisade mesophyll and the cells that make up the other areas within the leaf. 1) perpendicular arrangement 2) size 3) densely packed chloroplasts

17. How would the cylindrical shape of the palisade mesophyll cells increase the amount of photosynthesis that the leaf can carry out? The cylindrical shape can help more photosynthesis occur because more cells can be allowed inside which will allow more chloroplasts.

Photosynthesis: What’s in a Leaf?

3

18. What would be the advantage(s) to having no chloroplasts in the cells of the spongy mesophyll? Cells would be smaller, giving room for air spaces for gas exchange. There would also be veins needed there.

19. Suppose there were many chloroplasts in the cells of the upper epidermis. How would that change the amount of sunlight reaching the chloroplasts in the palisade layer? Less light would reach the palisade layer due to absorption in the epidermis.

20. Considering its locations and your previous knowledge of the word, what do you think might be the function of the epidermis? It provides protection and covers the inside of the leaf.

Read This! The cuticle covering the upper and lower epidermis of land plants is made of a waxy substance that repels water in much the same way as wax on a paper cup. 21. What is the purpose of having a water-tight covering? to keep the water in, which can maximize photosynthesis; reactants won't be taken out from inside the cells

22. Look carefully at the lower surface of the leaf in Model 2. a. What structure is found between guard cells? stoma

b. How would you describe this structure? an opening on the underside of a leaf to leave a gap between the guard cells

c. How would this affect the ability of the leaf to retain water especially in dry conditions? allows water vapor to escape leading to the leaf eventually drying out

4

POGIL™ Activities for High School Biology

23. Suggest a way in which the stoma and guard cells arrangement might work to control the amount of water that is leaving the leaf. the guard cells regulate the opening and closing of stoma

24. What is the relationship between the stoma and an air space? the stoma opens into the airspace inside the leaf

25. Looking back at Model 1, what gases might you find inside the air spaces? carbon dioxide, water vapor, oxygen

26. During the time that stomata (the plural of stoma) are closed, gases cannot enter or leave. Explain how this would affect the plant’s ability to do photosynthesis. If the stomata are closed, carbon dioxide cannot enter the leaf and photosynthesis will slow down because there isn't enough carbon dioxide.

27. How would the cuticle and stomata work together to maintain the leaf ’s function? The cuticle prevents the entire leaf from losing water from its surface and dehydrating. When the stomata closes, they prevent water loss from inside the leaf. The leaf is now totally sealed off.

28. In grammatically correct sentences, trace the path of the reactants for photosynthesis as they enter the leaf. Water and carbon dioxide enters the leaf cells. Sunlight energy powers photosynthesis as it enters through the cuticle and upper epidermis.

29. In grammatically correct sentences, trace the path of the products of photosynthesis as they exit the leaf. Once oxygen and sugar are made during photosynthesis, they are removed and transported to different locations. Sugars are carried by the veins out to the plant and oxygen diffuses into the environment through stomata.

Photosynthesis: What’s in a Leaf?

5

Extension Questions 30. Plants that live on the floor of forests tend to have much larger leaves than plants than live in hot, sunny conditions. Offer an explanation for this in which you refer to specific parts of the internal structure of a leaf. Plants of the floor of forests need large broad leaves to capture as much of the filtered sunlight as possible. Since photosynthesis mainly takes place in the palisade mesophyll, those cells are placed perpendicularly to the epidermis, having a large leaf would be an advantage because it could help capture more light to carry out photosynthesis.

31. Cacti are plants that live in extremely dry environments. Unlike most other plants, cacti do not have regular leaves, but instead have spines. They do have green stems. How would the lack of regular leaves help cacti survive in their environment? In what part of the cacti would photosynthesis occur? The lack of leaves would help the cacti conserve water for photosynthesis. Photosynthesis occurs in the thick stems of cacti.

32. Thinking about the structure and function of leaves, work with your group to propose modifications you might expect to see in the leaves of aquatic plants. Use the space below to make a sketch of the modified leaf, justifying what you include as well as what you leave out.

33. Use your knowledge of plant cell structure to answer each of the following questions: a. Where might water be stored for later use in the process of photosynthesis. in the central vacuole

b. What might plant cells do with the sugars made during photosynthesis? used in their mitochondria to produce energy for the cell to use

c. How does having cells with walls help a leaf to absorb as much energy as possible? cell walls give the leaf support so the leaf can be in a position to capture as much sunlight as possible

6

POGIL™ Activities for High School Biology...