The Structure of the Leaf and the Process of

Photosynthesis

Unit 4- Part 2

Mrs. Stahl

Leaves • Major site of photosynthesis / food production.

• Minimize water loss by collecting water and transpiration.

• Take in carbon dioxide and produce oxygen through the stomata.

• Stomas are tiny pores in the leaf.

• Protects stems and roots with shade and shelter.

Basic Structure • Blade- usually broad and flat; collects the

sunlight

• Petiole- stem that holds the leaf blade up.

4 Types of Plant Tissues

• 1. Ground Tissue- most common

• 2. Dermal Tissue

• 3. Vascular Tissue

• 4. Meristematic Tissue- division of new cells.

Covers the outside. Live parenchymal cells cover the outside, and have a cuticle (guard cells) Bark= dead cells

Makes up much of the inside. Provides support and stores materials in roots and stems. Packed with chloroplasts.

Transport water, mineral nutrients, and organic compounds to all parts of the plant. Xylem and phloem.

Ground Tissue most common and they differ

based on their cell walls- 3 Types

–1. Parenchyma

–2. Collenchyma

–3. Sclerenchyma

• The most common type of plant cell

• Store starch, oils and water

• Help heal wounds to the plant

• Found throughout the plant

Parenchyma Cells

–Provide support to a growing plant

–They are strong and flexible.

–They have unevenly thick cell walls.

Collenchyma Cells

–Strongest, support, very thick cell walls

–Second cell wall hardened by lignin

–Die when they reach maturity

–Used by humans to make linen and rope

Sclerenchyma cells

Meristematic Tissue

• Growth tissue

• Where cell division occurs

• Turns into ground, dermal, or vascular

• Apical Meristems- tips of roots and stems-> primary growth occurs here.

• Lateral Meristems- secondary growth. Increase the thickness of roots and stems.

Leaf Structure Let’s go inside!!!

Use your foldable of the leaf and the chloroplast for this portion of the

notes.

• 1. Cuticle: waxy coating, prevents water loss, decreases microbial penetration, and the amount of wax increases with light intensity exposure.

• 2. Upper Epidermis: no chloroplasts, provides a clear passageway for light to penetrate into the leaf.

• 3. Palisade Mesophyll: Filled with chloroplasts, performs more photosynthesis because it is closer to the top of the leaf.

• 4. Spongy Mesophyll: Contain chloroplasts and performs photosynthesis. Not as efficient as the palisade mesophyll.

• 5. Air Spaces: allow gases to be exchanged between the inside and outside of the leaf. Oxygen exits, CO2 enters.

• 6. Lower Epidermis: coats the bottom of the leaf (cuticle). Contains stomata for gas exchange. More stomata at the bottom of the leaf than at the top.

• 7. Stoma: allows for gas exchange. The opening and closing is regulated by guard cells.

• 8. Guard cells: help form the stoma. Inflate to open the stoma, or deflate to close the stoma.

• 9. Vascular Bundle (Vein): xylem & phloem surrounded by the bundle sheath. Passageways in the leaf, stem, and root of the plant.

• 10. Bundle Sheath Cells: surround the xylem and phloem, strengthen the veins, and protect the conductive tissues.

• 11. Xylem: transports water and minerals from the roots to the leaves.

• 12. Phloem: “food,” transports glucose and other products from the leaf to other parts of the plant for use or storage. Ex- sap.

The Chloroplast Diagram

• 13. Outer Membrane: semi-permeable, smooth, phospholipid membrane.

• 14. Inner Membrane: semi- permeable, phospholipid bilayer under the outer membrane.

• 15. Intermembrane Space: region between the outer and inner membranes.

• 16. Stroma: liquid in the inner chloroplast. Contains enzymes needed to catalyze the LDR (light dependent reactions) in photosynthesis.

• 17. Granum: “stack of pancakes,” stack of thylakoids

• 18. Thylakoid: houses the chlorophyll (pigment), which helps with photosynthesis. Light absorption (LDR). Contains accessory pigments, enzymes, and electron transport systems.

• 19. Thylakoid Lumen: the region located within each thylakoid.

• 20. Lamella: connect two or more grana to each other. Makes sure the grana are evenly spaced to maximize the ability to intercept sunlight.

The Importance of Guard Cells and Stomata

• The stomata is the site of transpiration and gas exchange.

• Guard cells surround each stomata, and open and close by changing shape.

• Day- stoma is open, allowing the carbon dioxide to enter and water to evaporate.

• Night- close

Guard Cells Open Stoma

• Allows CO2 necessary for photosynthesis to enter.

• Open due to potassium ions from neighboring cells accumulating in the guard cells, causing water to also enter the guard cells.

• Water evaporates from the leaves.

• Potassium ions accumulate in the guard cells and when there is a high concentration of K+ it causes water to flow into the cells. When the plant is full of water, the guard cells plump up and open the stomata.

Closed Stoma • When the plant is losing water

from leaves faster than it is gaining water at its roots, the guard cells deflate and close their stomata.

• May run low on CO2 and slow or stop photosynthesis.

• Stomata close at night.

Factors that cause the guard cells to open and close

• Temperature, humidity, hormones, and the amount of carbon dioxide in the leaves tells the guard cells to open and close.

Physiological Process of Transpiration,

Photosynthesis, and Cellular Respiration

Transpiration

• Evaporation of water from leaves

• Water is pushed up through the xylem by root pressure created from water moving up the soil to the plants root system and into the xylem-> results in small droplets of sap-> called guttation.

• Water is also pulled up through cohesion through the xylem tissue-> creates a negative pressure or tension from roots to leaves.

Rate of Transpiration

• Slows in high humidity

• Accelerates or speeds up in low humidity

• Increases with wind

• Increases with intense light= increased photosynthesis and water vapor

Photosynthesis

• Defined as the process that captures energy from sunlight to make sugars that store chemical energy.

• Location- Chloroplast of plant cells.

Chloroplast

Leaf Cell

Leaf

Photosynthesis • Chloro= Green

• Phyll= Leaf

• Plast = Molded

chloroplast

leaf cell

leaf

Two Processes

• Light dependent reactions= NEED SUNLIGHT

• Light independent reactions= OCCUR IN THE DARK

Equation

Chloroplast- refer to your foldable

• Three main parts are:

–Grana- stacks of coined shaped membranes.

Thylakoid – Inside the grana and they are the little disks.

They contain chlorophyll and other light absorbing pigments.

– Photosystems- light collecting units. They are proteins that organize chlorophyll and other pigments into clusters.

Add this onto your foldable.

Stroma

– Fluid that surrounds the grana inside the chloroplast.

• Chlorophyll- the molecule in the chloroplast that absorbs the energy from the sunlight. There are two main types, chlorophyll a and b, that absorb mostly red and blue light. Other pigments absorb the green.

• Green color in plants comes from the reflection of the green wavelengths by chlorophyll.

Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions.

When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through.

You do not

have to put

this in your

notes!!!

Just a little

fun fact!

Fall Foliage

So let’s begin

• The sunlight hits the leaves and CO2 is let in through the stomata (little pores) while H2O is let in through the roots.

Light Dependent Reactions or Light

Reactions – Requires sunlight

– Take place in the thylakoids

– Water and sunlight are needed

– Chlorophyll absorbs energy

– Energy is transferred along the thylakoid membrane, and then to light-independent reactions

– Oxygen is released as a waste product

Photosynthesis is broken down into two different reactions!!!

1st

Light Independent Reactions

• Uses the energy transferred from the light dependent reactions to make sugars.

• Reactions occur in the stroma

• Does NOT require sunlight

• Carbon dioxide is absorbed and used at this stage.

• Calvin Cycle- metabolic pathway found in the stroma of the chloroplast; where carbon enters in the form of CO2, and leaves in the form of glucose.

• ATP is produced as a final step. The enzyme ATP synthase is responsible for making ATP by adding phosphate groups to ADP.

2nd

Chloroplast

CO2 from the atmosphere

Energy carrying molecules transferred to the LIR

Glucose

Oxygen

Thylakoid

Sunlight entering

Calvin Cycle in the stroma

Chlorophyll

H2O

ATP & NADPH

Energy is transferred to electrons

Questions to review

• 1. Where do the light dependent reactions occur?

• 2. Where do the light independent reactions occur?

• 3. What two reactants are shown entering the chloroplast?

• 4. What two products are shown leaving the chloroplast?

• 5. What does the Calvin Cycle produce?

Answers

• 1. Thylakoid membrane

• 2. Stroma

• 3. Water and carbon dioxide

• 4. Oxygen and sugar

• 5. Glucose

Now that we have a brief overview let’s look at it in a little more detail.

Light Dependent Reactions • 1. Energy absorbed from sunlight and transferred to electrons

(electrons = energy) that enter the ETC. • 2. Water molecules are broken down; electrons enter

chlorophyll. • 3. Electrons jump from protein to protein down the ETC, and

their energy is used to pump the H+ ions from outside to inside the thylakoid membrane (against the concentration gradient = ACTIVE TRANSPORT)

• 4. Energy from sunlight continues to be absorbed, energizing electrons and pushing them along the ETC.

• 5. Electrons are then added to the molecule NADP+ (functions like ADP) to produce NADPH (functions like ATP).

• 6. H+ ions flow (diffusion) through a channel in the thylakoid membrane.

• 7. ATP is produced. ADP is changed into ATP when hydrogen ions flow through ATP synthase (enzyme).

Light Dependent Cont.

• Electron Transport Chain (ETC)- series of proteins in the membrane of the thylakoid.

• Energy-> electrons->ATP and NADPH (transferred to the later stages)

• Arrows represent energy and enzymes!

• NADP= coenzyme that can accept hydrogen and acts as an enzyme

http://www.biology-online.org/dictionary/Nicotinamide_adenine_dinucleotide_phosphate

Photosystem II captures and transfers energy.

Photosystem I captures energy and produces energy-carrying molecules.

Light Independent / Calvin Cycle

• Uses the ATP from light dependent reactions. ATP is crucial because without it the reaction would not happen.

• Does not need sunlight

• Occurs in the stroma and produces sugars

• Energy sources are ATP and NADPH

• Energy that is needed for a series of chemical reaction is called the Calvin Cycle, named after the scientist- Melvin Calvin.

• Rubisco is the enzyme used to set up the Calvin Cycle. It’s said to be the most abundant protein on Earth, but is much slower than most enzymes.

Light Independent Reactions

• 1. Carbon dioxide enters the Calvin Cycle, and are added to the already five carbons molecules that are there.

• 2. Energy is added. The six carbon molecules split to form three- carbon molecules. More energy is added (ATP & NADPH), and the molecules are rearranged into higher energy molecules.

• 3. A high energy three-carbon molecule exits for every 3 CO2 molecules that enter. After 2 three-carbon molecules have exited, they bond to form 1 six-carbon sugar.

• 4. Three carbon-molecules are changed back to five carbon molecules by energy from ATP.

Videos

https://vimeo.com/7316737 http://www.mhhe.com/biosci/bio_animations/02_MH_Photosynthesis_Web/ http://www.youtube.com/watch?v=lDwUVpOEoE4

Review Questions

• 1. Where do the light reactions occur?

• 2. Where do the electrons come from in the ETC?

• 3. What role do these electrons play?

• 4. What two energy carriers are produced?

• 5. When does active transport take place?

• 6. What enzyme speeds up the process?

• 7. Where in the chloroplast do light independent reactions occur?

• 8. Where do ATP and NADPH come from for the light independent reactions?

• 9. What does the LDR make? What does the LIR make?

• 10. How many cycles or turns does it take to make one glucose molecule?

• 11. What enzyme sets up the Calvin Cycle?

Answers • 1. Thylakoid membrane

• 2. Chlororphyll

• 3. Provide energy to move hydrogen ions into the thylakoid and to produce molecules of NADPH

• 4. NADPH and ATP

• 5. Step 3 when hydrogen ions are transported

• 6. ATP synthase

• 7. Stroma

• 8. LDR

• 9. LDR= makes ATP, LIR= makes sugars

• 10. 2

Let’s Summarize- Bellwork

Process Location Reactants Ending Products

Light Dependent Reactions Where the photosystems take place.

Light Independent Reactions. Where the Calvin Cycle takes place

Write the Equation for Photosynthesis

Let’s Summarize

Process Location Reactants Ending Products

Light Dependent Reactions Where the photosystems take place.

Thylakoid Membrane Sunlight H2O

ATP NADPH O2

Light Independent Reactions. Where the Calvin Cycle takes place

Stroma ATP NADPH CO2

Glucose

6CO2 + 6H2O -> C6H12O6 + 6O2