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55 Cards in this Set

  • Front
  • Back
What is the word equation for photosynthesis?

Carbon Dioxide + water = glucose + oxygen


(Equals sign should be an arrow)

How are water and mineral ions transported?

- Only available in soil


- Transport of water & mineral ions are essential to leaves


- Transported upwards in hollow tubes formed by dead cells called xylem tissue



How are products of photosynthesis (photosynthates) transported?

- Glucose produced (during photosynthesis) use to make sucrose and amino acids.


- Needed in organs of plant (flower, fruit..)


- Transported upward and downwards (bi-directional) in phloem tissue.



How are water & mineral ions taken up by the root?

- Mineral ions (Nitrates) are actively transported from soil to root hairs.


= Lowers water potential inside root hair cell so water is transported in by osmosis.


- Water & dissolved minerals ions travel through root cell of the cortex to endodermis down water potential gradient.


- Can take 3 different routes.


- When water & mineral ions reach endodermis forced to take symplast route by casparian strip.


- Casparian strip is made of suberin which impermeable to water molecules & mineral ions = apoplast pathway is blocked.

What are the 3 ways water is transported across the root?

1. Symplast route


2. Apoplast route


3. Vacuolar route

What is the apoplast pathway?

Water moves across the cortex, through cell walls.


- Fastest route.


- Stopped @ endodermis by casparian strip

What is the symplast pathway?
Water moves from the cytoplasm of the cells, through the plasmodesmata.
What is the vacuolar pathway?

By osmosis along a water potential gradient through vacuoles of adjacent cells.



Why does the plant need to control entry of mineral ions into the xylem (by Casparian strip)?
Some minerals are toxic if they absorbed & accumulate inside the plant tissue (copper ions).
Why do plants need to absorb nitrates?
RequIred for synthesis of amino acids, proteins, DNA, RNA & ATP.

Name some minerals (other than nitrates) that plants use?


Magnesium - Constituent of chlorophyll


Potassium - Required for stomatal opening


Phosphates - Synthesis of phospholipids


Give 2 features of root hair cells that are adaptions for uptake of water & mineral ions.

1. Large numbers of mitochondria to produce ATP for active transport of mineral ions.


2. Large surface area for osmosis & active transport.

What is transpiration?
The evaporation of water inside the leaves through the stomata to the atmosphere.
The Transpiration Stream...

- Water is absorbed by the root hair cells


- Water moves through root tissue, into the xylem & is transported up, through stem, to leaf.


- Water transported by cohesion from the xylem in leaf to cells of spongy mesophyll, where it evaporates from the surface of cells into the air spaces.


- Water vapour then diffuse out from the air spaces out of leaf through stomata down a water potential gradient.



What is cohesion?

- Water molecules are attracted to each other by hydrogen bonding (strong attraction exerted on one another)

What is adhesion?


Water molecules stick to the hydrophilic lining of the lignified xylem vessel walls.
What is capillarity?

- Forces of adhesion and cohesion which allow water molecules to rise up narrow tubes, for a short distance which is useful in small plants.


- After a short distance capillary action is opposed by gravity.

What is root pressure?

- Another force that helps to transport water upwards in the xylem.


- Caused by osmosis, as water moves from the endodermal cells of the root into the xylem.


- Active transport of minerals causes a pressure to push water upwards.

Describe the Cohesion-Tension Theory.

- As water diffuses out of stomata by transpiration, water molecules behind are pulled up to replace them.


- Drawn up leaf to xylem.


- Possible because of cohesion between water molecules du to hydrogen bonds & adhesion between water molecules & xylem vessel walls.


- Upward movement creates tension.

What 4 factors affect transpiration?

1. Temperature


2.Air Speed


3. Humidity


4. Light Intensity

How does temperature affect transpiration?

- Increased temp = increased rate of transpiration


- Increased temp = more kinetic energy of water molecules & increases rate of evaporation and diffusion


- Water potential is also lower in high temps.


= increases water potential gradient

How does air speed affect transpiration?

- Increased air speed = increased rate of transpiration


- Air movement blows away diffusion shells = higher water potential gradient.

How does humidity affect transpiration?

- Increased humidity = decreases rate of transpiration


- Water potential gradient between outside & inside leaf will decrease.



How does light intensity affect transpiration?

- Increased light intensity = increases rate of transpiration


- Light causes stomata to open to allow gas exchange for photosynthesis.

What does the potometer measure?
The rate of uptake of water by the shoot which indicates the rate of transpiration.

How to set a potometer?


1. Cut a leafy shoot under water - to prevent air bubbles entering xylem.


2. Completely fill apparatus w/ water to prevent entry of air.


3. Fit leafy shoots & seal all joints w/ Vaseline to make = apparatus is airtight.


4. Pat leaves dry - to prevent water potential gradient being reduced.


5. Introduce air bubble into capillary tube.


6. Measure the distance the air bubble moves along the scale in specific time.


- Distance / time


How do you calculate the volume of water in the capillary tube (potometer)?

π r (squared) x height


r = internal radius if the capillary tube

What does the xylem transport?


Water & mineral ions


4 Types of cell in in Xylem Tissue:

1. Vessels - Main cells that conduct water (lignin lined walls).


2. Tracheids - Also conduct water but less efficient than vessels & have long tapering ends.


3. Fibres - No role in transport (support only)


4. Xylem Parenchyma - Living tissue.

Talk about xylem vessels...

- Made of a continuous column of dead cells arranged end to end.


- Cross-wall between them dissolve = long, hollow tube that can transport large volumes of water.


- Have secondary cell wall thickened w/ lignin = impermeable to water & solutes


- Lignin also provides strength & mechanical structure = stops vessel collapsing under pressure.

Similarities between vessels & tracheids

- Both have lignin impregnated walls.


- Have perforations in the side of their walls called pits = allows sideways movements of water between adjacent cells.



Why is it important that xylem vessel walls are impermeable to water & solutes?
So the water & solutes don't fall out or the vessels would be useless.
Lignin is hydrophilic, why is that important for the xylem function?
So adhesion will occur between water molecules and the xylem wall.
What does the phloem transport?
Sucrose & amino acids
4 types of cell of the phloem?

Sieve tubes - Transport sucrose & amino acids up/ down the phloem.


Companion cells - Connect to sieve tube via the plasmodesmata & produce ATP for the sieve tube.


Phloem fibres - For support


Phloem parenchyma - Living tissue

Talk about the sieve tubes...

- Transports photosynthates


- Sieve tubes are formed from sieve elements placed end to end.


- Thin cellulose walls @ ends are perforated to allow cytoplasm from one cell to run to the adjacent one.


- They lose their nucleus and other organelles as they mature - companion cell is very useful to them.

Give 3 ways the sieve tube elements are adapted to their functions.


1. Few organelles = more space for the transport of solutes.


2. Have companion cells = provide ATP for them.


3. Perforated end walls (sieve plates) = allows passage of dissolved solutes.


What is translocation?

It is the transport of soluble organic materials produced by photosynthesis, in the phloem.


- Movement of molecules is bi-directional.


- Liquid inside phloem is called sap.

What is a source and give an example?

A region where the products of photosynthesis are produced & exported.


E.G Leaf

What is a sink and give examples?

A region where the products of photosynthesis are stored or used for growth.


E.G Roots, shoots, flower, fruits & seed

3 Ways of collecting evidence for translocation?

1. Ringing Experiments


2. Aphid Experiments


3. Radioisotope Labelling

What are ringing experiments (translocation)?


- Removal of the outer bark tissue from woody stem = removes phloem.


- Analysis of the phloem contents just above & below the ring shows photosynthates cannot be transported pass the region where the bark has been removed.


- Bulge is shown due to accumulation of sap that cannot move any further.


This shows:


1) The phloem is located just under the bark.


2) Transport can be downards


Explain the Aphid Experiments.

- Aphid s are small insects that can be used to collect the contents of the individual phloem sieve tube cells.


-The contents can be chemically analysed.


- Aphids have specialised mouthparts, stylets, which can penetrate the sieve tube to feed on sap.


- Aphids are anaesthetised w/ carbon dioxide & cut off so stylet remains in the stem.


- Stylets can be collected for analysis.


- More accurate than man w/ needle as the aphid's enzymes ensure that the stylet doesn't get blocked.

Explain radioisotope labelling.

- Supply radioactive Carbon dioxide (using carbon 14) to one leaf.


- After 20 mins the whole plant is placed on photographic film.


- Dark areas on the film negative show areas containing radioactivity.


- Results show that radioactive carbon is fixed into sugar produced @ the source during photosynthesis.


- It is the translocated to sink parts of the plant.


-Technique shows that sugars are transported bi-directionally since the radioactivity is seen in aerial parts of plants as well as the roots.

What is the Mass Flow Hypothesis & how does it work?

Theory to explain translocation = the passive flow of sugars from area of high concentrations (source) to area of low concentrations (sink).


1. Photosynthesis produces organic molecules including sucrose, in the source.


2. Sucrose is loaded by active transport into the sieves tubes (uses ATP).


3. Water enter the sieve tube, along the concentration gradient, by osmosis.


4. Pressure in sieve tubes increases & the sucrose solution moves through the phloem to the sinks.


5. Sucrose is unloaded by active transport into cells @ the sink. Sucrose is used for respiration to provide ATP for growth & cell division or maybe converted to starch for energy storage.


6. Water moves by osmosis out of the phloem as sucrose is removed & the pressure in phloem tissue is lower in the sink.


7. Pressure difference between source & sinks that maintains the movement through the phloem.



Arguments against the Mass Flow Theory


1. No explanation of sieve plates which seem to act as barriers to flow.


2. Sucrose & amino acids have been observed moving @ different rates and different directions.


3. Phloem has a high rate of ATP consumption, & translocation is slowed or stopped if respiratory inhibitors (cyanide) are added.


4. The companion cells contain numerous mitochondria for production of ATP.


Alternative theories for Mass Flow.

- An active transport may be involved.


- Streaming the cytoplasm of sieve tubes could be responsible for the bi-directional movements.


- Protein filaments have been observed passing through the sieve pores, suggesting different solutes are transported by different filaments.

What are mesophytes?

Most plants in temperate regions & most crop plants are mesophytes.


- Grow best in well drained soils & moderately dry air.


- Number of plant behaviours allow mesophytes to survive @ unfavourable times of the year.


E.G


Deciduous trees - Shed leaves in the autumn & regrow in spring.


Non-woody plants - Produce bulbs & corms to store sugar for when leaves & flowers die off.


Annual Plants - Before their wintery death, they produce seeds which lie dormant until spring.

What are hydrophytes?

Water plants that live submerged or partially submerged in the water.


E.G Lily pads.

Features of hydrophytes & explanation of it.


1. Little lignin in plant tissue - water is a supportive medium, so not required for support in the xylem.


2. Xylem tissue poorly developed - It is surrounded & submerged in water.


3. Leaves have thin cuticles - It is surrounded by water so there is no need to reduce water loss.


4. Stomata on upper epidermis of leaf - To allow gas exchange w/ the atmosphere ( air above)


5. Stems & leaves have large air spaces - Reservoir of oxygen & carbon dioxide for gas exchange & aids buoyancy.


What are xerophytes?

- Adapted to conditions of low water availability.


- They live in hot, dry desert conditions, or cold regions where soil is frozen for much of the year, or exposed to windy conditions.

Features of the xerophyte, Marram Grass.


1. Rolled Leaves - Reduces leaf's surface area from which transpiration can occur.


2. Sunken Stomata - Humid air is trapped in the pits = decreased diffusion of water vapour from the leaf to atmosphere.


3. Hairs on the surface of leaf - Hairs trap water vapour so there is a reduced diffusion gradient between the inside & outside of leaf.


4. Thick cuticle - Reduces water loss from epidermis.


Describe the xerophytic adaptation of cacti.

1. Thick waxy cuticles & succulent stem.


2. Spine - reduce surface area for transpiration.


3. Extensive roots - maximise water absorption.

Why do pine trees have needle like leaves?
Greatly reduces the SA of leaf available for water loss by transpiration.
Why do many xerophytes open stomata @ night & close them during the day?
To conserve water