section 12 leaf structure photosynthesis

7/21/2019 Section 12 Leaf Structure Photosynthesis

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Leaf Structure and

Photosynthesis


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DESIGN FEATURES FOR A LEAF

Exposed to sunlight

Large surface area

Capable of exchanging gasesCO2in, O2out


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DESIGN FEATURES FOR A LEAF

Import minerals and water

Not obtained from atmosphere

Export fixed carbon to sinks

Control water loss


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A TYPICAL LEAF


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THE LEAF BLADE

Broad expanded part of the leaf frequently has

the following features:

Large surface area

Thin with a small distance between upper and

lower surfaces
http://www.arscives.com/images/leaf-structure.jpg


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THE LEAF BLADE

These anatomical features:

Maximize the surface area while minimizing volume

Reduce the distance that gases must diffuse

through the leaf

Leaf structure varies to allow plants to survive and

grow under diverse conditions.


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LEAF TISSUES - EPIDERMIS

Epidermis

epi - upon

dermis - skin

The outer layer of cells

Comprised of a number of different cell types


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LEAF EPIDERMIS

Epidermal cells usually lack chloroplasts

Epidermis is also covered by a waxy cuticle

Impermeable to water


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STOMATA AND GUARD CELLS

Stomata are pores in the epidermis that lead to

intercellular spaces in the leaf (from the Greek

stoma, meaning mouth)

Found on both upper and lower surfaces of the

leaf

Formed by specialized guard cells


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STOMATA AND GUARD CELLS

Crescent shaped cells

When guard cells are turgid, stomata are open;

pores close when cells are not turgid


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WHY ARE STOMATA IMPORTANT FOR

PHOTOSYNTHESIS?

Some plants open stomata during the day,

close them at night

Some plants can fix CO2 at night (stomata

open) in order to minimize water loss during the

day (CAM)


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MESOPHYLL TISSUE

Occupies most of the internal tissue of the leaf

Comprised of two cell types

Palisade parenchyma cells

Spongy parenchyma cells


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MESOPHYLL TISSUE

Palisade parenchyma cells

Elongated cells

Contain many chloroplasts

Primary site for photosynthesis


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MESOPHYLL TISSUE

Spongy parenchyma cells

More randomly arranged

Air spaces between cells

Fewer chloroplasts


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VASCULAR TISSUE

Visible as veins distributed throughout the leaf

Required for transport of material to and from

the leaf


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VASCULAR TISSUE

Xylem

Distribution of water and minerals transported from

root

Phloem

Transport of fixed carbon compounds from the leaf

to the rest of the plant


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VASCULAR TISSUE


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PowerPoint Lectures for

Biolog y: Concepts and Connect ions , Fif th Edi t ionCampbel l, Reece, Taylor, and Simon

Lectures by Chris Romero

Photosynthesis: Using Light to Make FoodMAKIPHO

PHOTOSYNTHESIS


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Plant Power

Photosynthesis makes sugar and oxygen gas from

carbon dioxide and water

Carried out by plants, algae, and some bacteria

The ultimate source of all food eaten by animals

A major source of heat, light, and fuel


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AN OVERVIEW OF PHOTOSYNTHESIS

Autotrophs are the producers of the biosphere

Autotrophs produce their own food

Photoautotrophs produce organic molecules using

light energy

Plants, algae, and photosynthetic bacteria


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Photosynthesis occurs in chloroplasts

In plants, photosynthesis occurs primarily in leaves

CO2enters and O2exits

Chloroplasts are the site of photosynthesis

Concentrated in mesophyll cells of leaves

A protein molecules with a magnesium compound linked

to it. (important to know)


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Chloroplast structure

Stroma

Location of sugar synthesis

Thylakoids

Interconnected sacs

Contain chlorophyll in membranes

LE 7-2


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Leaf

Leaf Cross Section Mesophyll Cell

Vein

Mesophyll

Chloroplast

Stoma

Stroma

Chloroplast

CO2 O2

Granum

Grana Stroma

TEM9,750

Thylakoid Thylakoid space

Intermembrane

space

Inner

membrane

Outer

membrane

LM2,600


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Plants produce O2gas by splitting water

Photolysis


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ADP &

NADP

ATP &NADPH

CO2& H2O

(CH2O)

O2

H2O

Light Chlorophyll

LIGHT

REACTION

CALVIN

CYCLE

PHOTOSYNTHESIS

Photosynthesis can be described in this series

of coupled reactions:


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LIGHT REACTION

Occur in thylakoid membranes

Convert light energy to chemical energy as ATP and

NADPH

Produce O2as a waste product

LE 7-6A


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THE LIGHT REACTIONS: CONVERTING SOLAR

ENERGY TO CHEMICAL ENERGY

Visible radiation drives the light reactions

Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Gammarays X-rays UV Infrared

Micro-waves

Radiowaves

Visible light

Wavelength (nm)

650nm


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Several pigments are built into the thylakoids of

chloroplasts

Chlorophyll a

Absorbs blue-violet and red light, reflects green light


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Photosystems capture solar power

When a pigment molecule absorbs a photon

A H+electron is raised in energy

The electron releases excess energy as heat

Some pigments also emit light (bioluminescence)

LE 7-8B
http://upload.wikimedia.org/wikipedia/commons/e/e8/PanellusStipticusAug12_2009.jpg


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Electron transport

chain

NADPH

ee

e

e

Photosystem II Photosystem I

e

e

e

ATP


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CALVIN CYCLE

Occurs in stroma

Assembles sugar molecules from CO2using ATP

and NADPH from light reactions


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THE CALVIN CYCLE: CONVERTING CO2 TO

SUGARS

ATP and NADPH power sugar synthesis in the

Calvin cycle

LE 7-10A


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Input

CO2

ATP

NADPH

CALVINCYCLE

Output: G3Pglucose


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PHOTOSYNTHESIS REVIEWED AND EXTENDED

Review: Photosynthesis uses light energy tomake food molecules

The light reactions

Capture light energyGenerate NADPH and ATP

Release O2and water

The Calvin cycle

Manufactures sugarCells use many of the same mechanisms in

photosynthesis and cellular respiration


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PLANT USE OF GLUCOSE - ASSIMILATION

Glucose

Sucrose for

transport

Starch for

storage

Cellulose

For cell walls

Proteins

And DNA

Lipids-

Oils in seeds

chlorophyll

Magnesium

Ions from soilMineral ions

from soil

(nitrogen & phosphates


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PLANT USE OF GLUCOSE

Glucose is moved from the leaves to sinks

(growing areas)

This movement of glucose is referred to as

Translocation


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FACTORS AFFECTING PHOTOSYNTHESIS

Limiting factors are components of a reaction

that is in shortest supply

This can be used to help or hinder plant growth


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Deciduous trees loose their leaves during the

cooler parts of the year.


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The loose of leaves can sometimes be

described as an ex retory pro ess


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Mineral Nutrients

- Nitrate

- Phosphate

- Potassium

- Magnesium


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Nutrient ions are critical for plant growth and

development

A shortage of a particular mineral results in

particular symptoms called mineral deficiency

disease


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NITRATES

Used in amino acids, proteins, chlorophyll, DNA

and other compounds

Deficiency symptoms are stunted growth of

plant, older leaves turn yellow


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PHOSPHATES

Use in making DNA and many other

compounds; part of the cell

membrane

Deficiency symptoms are poor root

growth; young leaves turn purple


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POTASSIUM

Needed for enzymes of respiration and

photosynthesis to work

Deficiency symptoms leaves turn yellow with

dead spots


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MAGNESIUM

Used as part of the chlorophyll molecule

Deficiency symptoms leaves turn yellow
http://www.forestryimages.org/images/768x512/5373226.jpg


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Questions 37 and 38 on your own

section 12 leaf structure photosynthesis

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