Plant Nutrition Plant Diet Lets discuss So what

Plant Nutrition

Plant Diet? ?

Let’s discuss… So, what comes to mind when you hear of ‘Plant Nutrition’?

Show Time! Collection of documentaries on plants: • Plant Nutrition – http: //www. youtube. com/watch? v=Qa. FRb. Wsu. Wy. A (3 m) • Giant Water Lilies – http: //www. youtube. com/watch? v=igkjcuw_n_U (4 m) • Plants in harsh conditions • Quiver Tree – http: //www. youtube. com/watch? v=A 6 L 3 korq. Xb 4 (2 m) • Desert Plants & Cacti – http: //www. youtube. com/watch? v=EE 5 jd 4 br. XU&feature=related (4 m) • ‘Parasitic’ Plants • Strangler Figs – http: //www. youtube. com/watch? v=UCUtpmwaco. E (3. 5 m) • Jungle Climbers – http: //www. youtube. com/watch? v=H 9 MV 5 Cg. Pg. IQ (3 m) • Carnivorous Plants • Pitcher Plant – http: //www. youtube. com/watch? v=tr. Wz. Dl. Rvv 1 M (4 m) • Venus Fly Trap – http: //www. youtube. com/watch? v=kt. IGVt. Kdgwo (3. 5 m)

Topic Overview Week 4: Leaf Structures & Functions • Intro to plant nutrition • Leaf structures and functions – External – Internal • The role of guard cells • How CO 2 and water enter the leaves

Topic Overview Week 5: Photosynthesis • 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

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 CO 2 and water by plants

External Structure of a Leaf • 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

Internal Structure of a Leaf

The Main Components • 3 layers 1. 2. 3. Upper Epidermis Mesophyll Lower Epidermis 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

Mesophyll • Region between the upper and lower epidermis • Consists of two layers of tissue 1. 2. Palisade mesophyll Spongy mesophyll Can you spot the differences between these two layers of cells? !

Palisade vs. Spongy 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

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 CO 2 to dissolve in

Lower Epidermis • 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

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?

Dark Light

Opening of Stomata 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

Closing 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

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 CO 2 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. CO 2 is rapidly used up for photosynthesis 4. Concentration of CO 2 in leaf decreases – generates a diffusion gradient

How does CO 2 enter the leaf? 5. Atmospheric CO 2 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

Test Time! biology. clc. uc. edu x 400

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?

Origin of Our Energy • 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 producers Can you recall why?

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 O 2 (for aquatic plants)

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

Experiments on Photosynthesis Chlorophyll Questions asked: 1. Is sunlight required for photosynthesis? 2. What about chlorophyll? 3. And carbon dioxide? 4. What gas is emitted during photosynthesis?

Experiment 1 Does 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

Experiment 2 Does photosynthesis require chlorophyll? • Test for the necessity of chlorophyll for plants to carry out photosynthesis • Use plant with variegated leaves • Destarch and place plant in sunlight • Test for starch and note the distribution of stain

Experiment 3 Does photosynthesis require carbon dioxide? • 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 3 Setup Does photosynthesis require carbon dioxide?

Experiment 4 What gas is emitted during photosynthesis? • 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 4 Setup What 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

Summary • 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?

WWW Resources • http: //www. explorelearning. com/index. cfm? method=c. Res ource. dsp. View&Resource. ID=395 • http: //www. ext. vt. edu/resources/4 h/virtualforest/