Plant Nutrition

Plant Diet?

?

So, what comes to mind when you hear of

‘Plant Nutrition’?

Let’s discuss…

Show Time!

Collection of documentaries on plants:

• Plant Nutrition – http://www.youtube.com/watch?v=QaFRbWsuWyA (3m)

• Giant Water Lilies – http://www.youtube.com/watch?v=igkjcuw_n_U (4m)

• Plants in harsh conditions• Quiver Tree – http://www.youtube.com/watch?v=A6L3korqXb4 (2m)

• Desert Plants & Cacti – http://www.youtube.com/watch?v=E-E5jd4brXU&feature=related (4m)

• ‘Parasitic’ Plants• Strangler Figs – http://www.youtube.com/watch?v=UCUtpmwacoE (3.5m)

• Jungle Climbers – http://www.youtube.com/watch?v=H9MV5CgPgIQ (3m)

• Carnivorous Plants• Pitcher Plant – http://www.youtube.com/watch?v=trWzDlRvv1M (4m)

• Venus Fly Trap – http://www.youtube.com/watch?v=ktIGVtKdgwo (3.5m)

• Intro to plant nutrition

• Leaf structures and functions– External– Internal

• The role of guard cells

• How CO2 and water enter the leaves

Topic Overview

Week 4: Leaf Structures & Functions

• The basics & importance of photosynthesis

• Test for starch in leaves of plants

• Factors affecting the rate of photosynthesis

• The limiting factors of photosynthesis

• 2 stages of photosynthesis

• Uses of glucose by the plants

Topic Overview

Week 5: Photosynthesis

Aims of Today’s Lesson

At the end of this lesson, you should be able to

• Identify and label the cellular and tissue structure of a leaf

• Describe the significance of these features in terms of their functions:

– Distribution of chloroplasts in photosynthesis– Stomata and mesophyll cells in gaseous exchange– Vascular bundles in transport

• Outline the intake of CO2 and water by plants

• 4 main features

1. Lamina– Large flat surface ensures maximum amount of sunlight

absorbed– Thin lamina facilitates rapid diffusion of gases into and

out from the inner cells

2. Petiole– Holds lamina away from the stem to obtain max.

sunlight and air for leaf

3. Network of veins– Carry water, minerals and food to and fro

4. Leaf arrangement– Dispersed (away from each other) ensures optimal

absorption of sunlight

External Structure of a Leaf

External Structure of a Leaf

Internal Structure of a Leaf

• 3 layers

1. Upper Epidermis

2. Mesophyll

3. Lower Epidermis

The Main Components

Let’s examine what is inside each of this layer!

Upper Epidermis

• Single layer of closely packed epidermal cells

• Covered by a waxy layer called the cuticle– Prevent excessive water evaporation– Protects the enclosed leaf tissue

• Transparent – allows sunlight to penetrate

• No chloroplasts

• Region between the upper and lower epidermis

• Consists of two layers of tissue1. Palisade mesophyll

2. Spongy mesophyll

Can you spot the differences betweenthese two layers of cells?!

Mesophyll

Palisade vs. Spongy Mesophyll

Palisade

• Have 1 or 2 layers of long cylindrical cells that are closely packed

• Contain numerous chloroplasts

Spongy

• Cells are irregular in shape

• Numerous large intercellular air spaces between them

• Fewer chloroplasts

Palisade vs. Spongy Mesophyll

• Large intercellular air spaces present in the spongy mesophyll allows for rapid diffusion of gases

• Photosynthesis still takes place in this layer, but to a lesser extent

• Presence of vascular bundles – xylem & phloem

Note! All cells in the palisade and the spongy mesophyll are covered with a thin film of moisture – for CO2 to dissolve in

Spongy Mesophyll

• Like the upper epidermis– Single layer of closely packed cells– Also has a waxy layer of cuticle (thinner) to prevent

excessive water loss– No chloroplasts

• Contains many tiny openings/pores called the stomata (singular: stoma)

• Important in gaseous exchange

Lower Epidermis

Stomata

• Tiny openings in the lower epidermis

• Allows gaseous exchange to take place

• Enclosed by two cells – guard cells – Bean-shaped– Contain chloroplasts

Guard Cells

• In most cases, stomata open in the light and close in the dark

• Guard cells are the only cells in the lower epidermal layer capable of making glucose

So what makes them open and close?

Light

Dark

In the presence of light…

• Photosynthesis takes place• Potassium ions are pumped into the guard cells via

active transport• Decrease in water potential in guard cells• Water from epidermal cells enters guard cells via

osmosis• Guard cells become turgid, swollen and more

curved pull the stomata open

Opening of Stomata

In the absence of light…

• Potassium ions diffuse out from the guard cells• Increased water potential in guard cells• Water leaves the cells by osmosis• Guard cells become flaccid stomata close

Closing of Stomata

Veins or Vascular Bundles

• Contains xylem and phloem

• Xylem transports water and mineral salts from the roots to the leaves

• Phloem transports sucrose and amino acids from leaves to the other parts of the plant

How does CO2 enter the leaf?

1. At night, carbon dioxide produced is stored in the air spaces of the leaf

2. In the day, rate of photosynthesis > rate of respiration

3. CO2 is rapidly used up for photosynthesis

4. Concentration of CO2 in leaf decreases– generates a diffusion gradient

5. Atmospheric CO2 diffuses into the leaf via the stomata

6. Carbon dioxide dissolves in the film of moisture

7. After which, it diffuses into the cells for photosynthesis

How does CO2 enter the leaf?

Test Time!

x400biology.clc.uc.edu

Summary

• How does the external structures of leaf help in carrying out photosynthesis?

• How many layers of cells are there in a leaf?

• How does each layer help in carrying out photosynthesis effectively?

• What is the purpose of the thin film of moisture that coats most cells of the leaf?

• How do the stomata open and close? Which cells are responsible for the opening and closing of the stomata?

Photosynthesis

Origin of Our Energy

How do we get our energy?

Recall the food you had for your breakfast or your dinner last night?

What is the similarity between the food that you and your classmates had eaten?

• The truth is our energy stems primarily from green plants

Why green plants in particular ?

• Green plants have the capability to make and store their own food food producers

Can you recall why?

Origin of Our Energy

Raw Materials and Conditions required for Photosynthesis

1. Sunlight

2. Chlorophyll

3. Carbon Dioxide

4. Water

Products of Photosynthesis

1. Food in the form of glucose

2. Oxygen

3. Water

Overall equation:

Chlorophyll

Plants do not use all the light that

illuminates them!

How to test for evidence of photosynthesis?

• Glucose is made during photosynthesis

• Excess glucose is converted to starch

• Presence of starch can be tested by conducting an iodine test

• Release of O2 (for aquatic plants)

Test for Starch

http://www.footprints-science.co.uk/Starch.htm

Experiments on Photosynthesis

Questions asked:

1. Is sunlight required for photosynthesis?

2. What about chlorophyll?

3. And carbon dioxide?

4. What gas is emitted during photosynthesis?

Chlorophyll

Experiment 1Does photosynthesis require sunlight?

• Test for the importance of sunlight for plants to carry out photosynthesis

• Main emphasis is to destarch the plants for 2 days (why?)

• Cover a portion of the leaf from sunlight and place the plant in sunlight for a few hours (control?)

• Test for starch

• Test for the necessity of chlorophyll for plants to carry out photosynthesis

• Use plant with variegatedleaves

• Destarch and place plant in sunlight

• Test for starch and note the distribution of stain

Experiment 2Does photosynthesis require chlorophyll?

• Test for the necessity of carbon dioxide for plants to carry out photosynthesis

• 2 setups (Plants in both setup must be destarched)

• One set up is a control, the other does not have carbon dioxide

• Place in sunlight and remove after a few hours

• Test for starch

Experiment 3Does photosynthesis require carbon dioxide?

Experiment 3 SetupDoes photosynthesis require carbon dioxide?

• Test for gas that is given off during photosynthesis

• Use of freshwater plants

• Dissolve sodium hydrogen carbonate in water (why?)

• Place in sunlight until gas bubbles appear

• Test for gas (how?)

Experiment 4What gas is emitted during photosynthesis?

Experiment 4 SetupWhat gas is emitted during photosynthesis?

How do you remember the details?

• All three except one experiment require plants to be destarched

• All plants are subjected to an iodine test

• Remember the control setup has the basic setup

• Why do we test for starch in leaves instead of glucose?

• How do we test for starch?

• What are the steps taken to test for starch in a leaf?

• When is there a need to destarch plants?

• What is the minimum period of time that a plant needs to be destarched?

Summary

• http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=395

• http://www.ext.vt.edu/resources/4h/virtualforest/

WWW Resources