Photosynthesis

Photosynthesis & LifeOccurs in the chloroplasts

Uses light energy to combine Water and Carbon dioxide into Starch and Oxygen

6H2O + 6CO2 + Sunlight = 6O2 + C^H12O6

Enzymes control the process which is a very complicated step by step process.

Chlorophyll is what makes the leaves green which absorbs blue and red light from the sun.

Total photosynthesis across the globe is about 200,000,000,000 tonnes of glucose a year this is turned into Cellulose

internal leaf structure

chloroplastsouter membrane

inner membrane

thylakoid

Chloroplasts

Light, temperature and availability of raw materials all affect the rate of photosynthesis

Brighter light increase the rate of photosynthesis. Therefore the rate of photosynthesis changes throughout the day.

The rate of photosynthesis doubles with 10oC increase of temperature up to a temperature of 40oC.

Lack of water will cause plants to wilt and stop photosynthesising.

The atmosphere is made of 0.03% CO2. If this changes the rate of photosynthesis also changes

Rate of Photosynthesis

Adaptations to cope

Because of all the environmental factors that affect photosynthesis plants are able to adapt to survive these.

The most important of these is water

Mesophytic plants like roses are very adapt at dealing with water shortages.

External Leaf adaptations

Surface area

Petiole and Veins

Cuticle

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Internal Leaf adaptations

Layers

Upper and Lower epidermis

Palisade mesophyll

Spongy mesophyll layer

Vascular bundles

H2O Water Vapor

GlucoseSunlight

O2

CO2

Gas exchangeStomata

During the day CO2 defuses into the cell and H2O and O2 defuse out

During the night and when respiration is happening CO2 defuses out and O2 defuses in.

Guard cells

If they absorb water they become turgid (swollen) and open the stoma.

Plant Transport

Recall

Transport MechanismPassive vs. Active

Plant Transport TissuesXylem

Phloem

Transport Mechanisms

Passive transportPassive Diffusion

Facilitated Diffusion

Osmosis

Active transport

Bulk transport

Plant Transport Tissues

XylemVessel elements

Tracheids

PhloemSieve tube member

Companion cells

Problem of Terrestrial Plants

Ancestral plants: transport is through diffusion

Modern plants: transport from roots to shootsLong distance transport

Figure 36.1

Transport in Plants

Three scales of plant transportIntracellular

Epidermal cells

Short distance: cell-to-cellAt the levels of tissues and organs

Long distance: xylem and phloem

MineralsH2O CO2

O2

CO2 O2

H2O Sugar

Light

A variety of physical processesAre involved in the different types of transport

Sugars are produced byphotosynthesis in the leaves.5

Sugars are transported asphloem sap to roots and otherparts of the plant.

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Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon forphotosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

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Transpiration, the loss of waterfrom leaves (mostly through

stomata), creates a force withinleaves that pulls xylem sap upward.

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Water and minerals aretransported upward from

roots to shoots as xylem sap.

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Roots absorb waterand dissolved minerals

from the soil.

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Figure 36.2

Roots exchange gases with the air spaces of soil, taking in O2 and discharging CO2. In cellular respiration, O2 supports the breakdown of sugars.

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Effects of Differences in Water Potential

To survivePlants must balance water uptake and loss

OsmosisDetermines the net uptake or water loss by a cell

Is affected by solute concentration and pressure

Water potentialIs a measurement that combines the effects of solute concentration and pressure

Determines the direction of movement of water

WaterFlows from regions of high water potential to regions of low water potential

Both pressure and solute concentrations affect water potential

Water potentialAffects uptake and loss of water by plant cells

If a flaccid cell is placed in an environment with a higher solute concentration

The cell will lose water and become plasmolyzed

Plasmolyzed cellat osmotic equilibriumwith its surroundings

If the same flaccid cell is placed in a solution with a lower solute concentration

The cell will gain water and become turgid

Distilled water:

Initial flaccid cell:

Turgid cellat osmotic equilibriumwith its surroundings

Figure 36.6b

Bulk Flow in Long-Distance Transport

In bulk flowMovement of fluid in the xylem and phloem is driven by pressure differences at opposite ends of the xylem vessels and sieve tubes

The xylem sap and phloem sap

Xylem sapRoot pressure

Transpiration-cohesion-tension mechanism

Phloem sapPressure Flow Theory

Translocation

Turgor Pressure

This is what happens when plants don’t have enough water

Turgor pressure is when water presses on the cell wall – inflating the cell

Soft plants have lots of soft tissue that needs a regular supply of water

Vascular Bundles

• The vascular system is made of three sections

• Phloem• Xylem• Cambium

Root pressure

Root tip cells have a large number of tiny extensions called root hairs

Root hairs provide a huge surface area in the soil.

Water enters the root via osmosis?? – What happens as the water pressure builds up?

Transpiration pull

More than 90% of the water moving up a plant is lost through transpiration as water vapor through the stomata.

As the water leaves the the plants the concentration of solutes increases within the cells, this draws more water into the cells from the xylem

Phloem transport

Sugar and amino acids are transported from the leaves to pares of the plants requiring food through the phloem

The pressures gradient that moves this is created via the concentration of sugars

Dissolved food transport is called translocation