unit 9 photosynthesis in green plants science interactive ltd copyright 2005

Unit 9 Photosynthesis in Green Plants

Science Interactive LTD Copyright 2005

Understand: Keywords:1. The anatomy and cell parts of the common

plant cell.2. The role of the chloroplast and mitochondria

during photosynthesis and respiration.3. The role of the leaf and the palisade cell during

photosynthesis.4. That the substrates for photosynthesis are

water and carbon dioxide.5. That the products of photosynthesis are

glucose and oxygen.6. That light energy is essential for

photosynthesis to occur.7. That the overall rate of photosynthesis is

determined by limiting factors including carbon dioxide, light intensity, light colour and temperature.

8. That plants use glucose to make other molecules.

9. That plants can respond to stimuli like light, gravity and moisture.

Leaf, Tissue, Organ, Cell, Palisade, Photosynthesis, Substrates, Water, Carbon dioxide, Products, Glucose, Oxygen, Light, Energy, Intensity, Limiting, Factors, Light, Temperature, Colour, Rate, Tropism & Stimuli.

Unit 9: Photosynthesis in Green PlantsUnit 9: Photosynthesis in Green Plants

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Levels of organisation in plantsLevels of organisation in plantsIn plants, as in animals, similar cells performing similar f__________ are organised into tissues. Leaf palisade tissue consists of identical palisade cells functioning together to enable photosynthesis to occur. Other tissues found in green l________ also support photosynthesis. A leaf is an organ made up of many different tissues. Different organs work together as part of the entire plant organism. There are four distinct organs in a typical plant: The root system, the stem system, the leaf system and the reproductive system. Name the function of each of the four organ systems found in green plants ?

Cells, tissues, organs and organ systems in plants:


Word bank: functions leaves

Cells Tissues Organs Organism

Diagram

Notes Cells are highly specialised and are designed to do their job within the plant. List 3 specialised cells found in green plants ?

Tissues like the palisade layer or stomata tissue are a collection of cells working together to perform specific tasks in the plant.

Organs are a collection of tissues like the leaf. Many separate organs build an organ system. List 3 organs in the plant ?

The are four organ systems that support life in plants. All perform specific roles. Which of these systems does not support photosynthesis ?

Plant leaf system Plant leaf system A number of cells and tissues within the plant leaf play a role during photosynthesis, whereby water and carbon dioxide combine during photosynthesis to form g_______ and o_________. Palisade cells containing chloroplast are the main site of glucose production. Xylem tissue supplies water from the root and phloem tissue transports glucose made during photosynthesis around the plant. Gaseous exchange during photosynthesis and respiration is controlled by the stomata cells. Why are the stomata cells found only on the underside of the leaf ?

Plant leaf system:

A

B

C

DE


Word bank: glucose oxygen

Stomata cells Xylem tissue Plant leaf Leaf system

Diagram

Notes Stomata found on the underside of the plant leaf allows gaseous exchange and water transpiration. They open during the day and remain closed during the night.

The xylem tissue transports water and minerals like nitrates from the root system to the leaf system via the plant stem. Phloem tubes transport sugary sap all around the plant.

The leaf is a collection of tissues:A: Upper epidermis

B: Palisade layer

C: Spongy mesophyll

D: Lower epidermis

E: Stomata

The leaf system is a collection of leaves that work together producing glucose and oxygen from water and carbon dioxide using the energy from the sun during daylight hours.

Specialised cells in plantsSpecialised cells in plantsLike animals, plants have many different s____________ cells performing different functions. Green plants have many examples of specialised cells that are designed for functions like photosynthesis, growth, reproduction, taking in w______ and minerals from the soil. The leaf palisade cell is a good example of a specialised cell in plants. It is well designed for photosynthesis, for example it contains many chloroplasts organelles, rich in chlorophyll. Where is the palisade tissue located in the plant ?

Specialised cells:


Word bank: specialised water

Palisade cell Root hair cell Stomata cell Pollen cell

Diagram

Notes Green leaves contain many palisade cells which are rich in chloroplasts that enable photosynthesis to occur. Why do root cells not have these cell parts ?

The root hair cell has a large surface area to volume ratio, so that it can absorb water and minerals from the soil. Name two of these mineral salts found dissolved in water ?

The stomata cells controls the exchange of CO2 and oxygen during photosynthesis. They close during the night. At what time during the day does CO2 enter the leaf ?

Pollen cells, normally transferred to the female carpel by bees and other insects carry genetic information to create a new plant when it fuses with the female ovule.

The common plant cellThe common plant cellPlant cells, like animals cells are made from many cell parts or organelles, each with a specific function. The common plant cell has some similarities and some differences to animal cells. This reflects differences in the way plants and animals feed and support themselves. The most important cell part is green c____________ containing chlorophyll which allows photosynthesis to occur.

Common plant cell:


Word bank: chloroplast

Cell part Function (complete)

Nucleus Control cells activities and contains DNA

Cytoplasm _______________________ ?

Membrane _______________________ ?

Vacuole _______________________ ?

Cell wall _______________________ ?

Chloroplast _______________________ ?

Mitochondria _______________________ ?

Lysosome _______________________ ?

Mitochondria and chloroplast organellesMitochondria and chloroplast organellesIf you view plant and animals cells under a microscope, you can see tiny dots in the cytoplasm. These are the mitochondria. Cellular r____________ occurs in the mitochondria, releasing energy from glucose molecules. Plants also have green c____________ containing chlorophyll where water and carbon dioxide are combined to form glucose and o_________ during photosynthesis. Why do muscle cells contain more mitochondria than skin cells ?

Mitochondria and chloroplast:

Membrane

Membrane

Matrix

Matrix


Word bank: respiration chloroplast oxygen

Mitochondria Chloroplast

Diagram

Function in the cell To respire glucose with oxygen providing cell energy. All living cells have these organelles.

To produce glucose using CO2 and water. All green plants have these organelles.

Equation C6H12O6 + 6O2 6H2O + 6CO2 6H2O + 6CO2 _____ + _____

Animal or plant Animal and plant Plant only

Plants as producersPlants as producers oneone

Plants are called producers because they produce all the World’s biomass via a process called photosynthesis. Plants use energy from the s_____ to combine carbon dioxide and w________ to form g__________ and oxygen. This reaction produces millions of tonnes of living matter that nourishes all other living organisms in the animal kingdom. The oxygen that plants release into the atmosphere is used in cellular r_____________ by all living organisms. How can we determine the biomass of a plant ?

Plants as producers:


Word bank: sun water glucose respiration

Plant yield: (kg per hectare)

14000

10000

6000

2000

<1000

C6H12O6

6O26CO2

6H2O

Plant cells

Chloroplast

EnergyGlucose

Photosynthesis in action Plant yield

Diagram

Notes Green chlorophyll contained in palisade chloroplasts are able to use light energy to enable carbon dioxide and water to combine to form glucose and oxygen.

Plants only use a small fraction of the sunlight energy, they receive every year. Despite this, sugarcane produces up to 200 tonnes of glucose per year per hectare. The most productive areas are the equatorial regions that receive the most sunlight energy.

Plants as producersPlants as producers twotwo

The glucose produced during photosynthesis in green plants is used to make plant c____________, lipids and proteins. Every year over 70,000,000 kJ of sunlight energy falls on every metre squared of land. Plants only use about 90,000 kJ/m2/year of l_______ energy during photosynthesis, however they produce over 132 billion tonnes per annum of biomass. Overall plant yields depend on a number of factors including light availability, soil quality, rainfall levels and competition. How could you determine the yields of different crops over time ?

Plant yield and biomass:


Word bank: carbohydrates light

Crop Sugarcane Corn Rice Wheat

Diagram

Notes Sugarcane, rich in glucose can produce a yield of up to 9000 kg per acre.

Corn, rich in proteins and carbohydrates can produce a yield of up to 5500 kg per acre.

Rice, rich in carbo-hydrates can produce a yield of up to 3000 kg per acre

Wheat, rich in carbo-hydrates and sugars can produce a yield of up to 2500 kg per acre.

Plants as producersPlants as producers threethree

Plants are extremely efficient at transforming the energy carried by light to chemical energy trapped in glucose molecules, which are produced during p_____________. Their efficiency is about 80%, far higher than typical values for herbivores and carnivores. Only a small fraction of the c__________ energy they produce in the form of glucose is lost through respiration or waste. How could you determine the amount of glucose that is used during cellular respiration in plants ?

Plants using light energy:

1

1

2

2

33

Biomass

Waste

Respiration

Biomass: Energy contained in the tissues of the plant (available for the next level.)

Waste: Energy contained in the waste materials found in leaves.

Respiration: Energy used in cellular respiration by all plant cells.

8,000 kJ

1,500 kJ

500 kJ

Light energy

10,000kJ


Word bank: photosynthesis chemical

Plants use of light energy Process

Diagram

Notes The transfer of energy from the sun’s rays to the glucose found in plant leaves is achieved during photosynthesis. Plants are highly adapted and efficient at transforming light energy to chemical energy. Over 132 billions tonnes of plant biomass is produced globally every year.

Only a very small fraction of energy is used for respiration or lost as waste. Plants are almost 80% efficient as producers.

Plants as producersPlants as producers fourfour

Plant leaves contain many palisade cells containing green c___________. Palisade cells use e______ from sunlight during photosynthesis to make g________ and oxygen. This palisade cell layer is found near to the surface of the leaf. Here it can absorb all the sunlight that falls on the leaf’s surface. How could you design an experiment to show that light is an essential factor for photosynthesis ?

Plants using light energy:

A

B

C

D

E

FG

Anatomy of the plant leaf Process

Diagram A: Upper epidermis

B: Palisade layer

C: Spongy mesophyll

D: Lower epidermis

E: Stomata

F: Xylem

G: Phloem

Give a function of the leaf tissue.

Say how each part helps photosynthesis ?

Notes The transfer of energy from the sun’s rays to the glucose found in plant leaves is achieved during photosynthesis. Plants are highly adapted and efficient at transforming light energy to chemical energy. Over 132 billions tonnes of plant biomass is produced globally every year.

Only a very small fraction of energy is used for respiration or lost as waste. Plants are almost 80% efficient as producers.


Word bank: chloroplasts energy glucose

Parts of the leaf

Cuticle

Upper epidermis

Palisade layer

Spongy mesophyll

Lower epidermis

Stomata

Guard cells

Xylem

Phloem

Give a function for each tissue found in green leaves. Say how each part helps photosynthesis ?

Plants as producersPlants as producers fivefive

Every tissue found in green leaves, supports the production of glucose during photosynthesis. Palisade cells containing green c___________ have enzymes which use light energy to combine water and carbon dioxide forming glucose and oxygen. The xylem transports w______ from the root. Phloem tubes transport glucose to the rest of the plant. Stomata cells allows carbon dioxide from the atmosphere and promote transpiration. The spongy mesophyll allows carbon dioxide to diffuse quickly to the palisade cells. Why are the palisade cells filled with chloroplast found in the upper part of the leaf ?

Plants leaf structure and anatomy:


Word bank: chloroplast water

Photosynthesis, the process whereby l______ energy is used by palisade cells found in green leaves to combine carbon dioxide and water to produce glucose and oxygen. This is the equation for the whole process.

From the equation we can see there are three requirements: Light Chlorophyll Substrates: Carbon dioxide and water

Requirements for photosynthesis:

Photosynthesis and its equationPhotosynthesis and its equation oneone

Carbon dioxide + Water Glucose + OxygenLight and chlorophyll


Word bank: light

Carbon dioxide Water

Light Chlorophyll Carbon dioxide and water

Diagram

Notes Light is used to provide the energy required during photosynthesis to combine water and carbon dioxide producing glucose and oxygen.

Green chlorophyll found in the leaf palisade layers uses light energy to form glucose and oxygen. It contains a very complicated series of enzymes that act as catalysts.

Carbon dioxide, absorbed by the leaf and water absorbed by the root hair cells are essential substrates that are used during photosynthesis making glucose and oxygen.

Photosynthesis and its equationPhotosynthesis and its equation twotwo

From the equation for photosynthesis, we can determine the raw materials required during photosynthesis. Glucose production in green leaves will only occur if w_______ and carbon dioxide are supplied to the chloroplasts inside leaf palisade cells.

6CO2 + 6H20 C6H12O6 + 6O2

Carbon dioxide water light and chlorophyll Glucose Oxygen

Raw materials and photosynthetic products:

6 molecules of CO2 6 molecules of H2O 1 molecule of glucose 6 molecules of O2


Word bank: water

Substrate Carbon dioxide Water Glucose Oxygen

Diagram

Notes Carbon dioxide is taken in during day light hours through the leaf stomata cells from the atmosphere.

Water is taken from the soil by the root hair cells, through the xylem and into the leaf space.

Glucose produced during photosynthesis is transported by the phloem to all parts of the plant.

Oxygen is taken out through the leaf during daylight hours and released into the atmosphere.

Reactions that take in energy from their surroundings in the form of heat or light are called endothermic reactions. Although these types of reactions are not as common as exothermic reactions, there are several examples. An important example of an endothermic reaction is photosynthesis, whereby light e_________ is used to combine water and carbon dioxide to form glucose and oxygen.

Energy changes during photosynthesis:

Products

Substrates

C6H12O66O2

6H2O 6CO2

Activation energy Net energy taken in during reaction

Photosynthesis and its equationPhotosynthesis and its equation threethreeScience Interactive LTD Copyright 2005

Word bank: energy

Progress of reaction

Po

ten

tial

en

erg

y

O2

H2O CO2

C6H12O6

Photosynthesis in green plants Key

In this reaction H2O and CO2 substrates are combined in the plant leaf cells using light energy to produce glucose (C6H12O6) and O2.

Sunlight, carbon dioxide, water and g______ chlorophyll are all essential for photosynthesis to take place inside a green leaf. Proving that these are essential, however requires experimentation. A series of experiments were carried out and are summarised in the table below. In brief, plants with no access over 48 hours to sunlight, chlorophyll or carbon dioxide were tested for starch in their l________. For each experiment, complete the results and give an explanation ?

Factors required for photosynthesis:

CompleteComplete

Photosynthesis and its equationPhotosynthesis and its equation fourfour

1: No light 2: No chlorophyll 3: No carbon dioxide

Diagram

ResultsShow leaf after testing with iodine solution.

Explanation Starch is shown by a blue - black colour when in contact with iodine. What does this experiment prove ?

_______________________________________________________________________ ?

_______________________________________________________________________?


Word bank: green leaves

Limiting factors for photosynthesisLimiting factors for photosynthesisFrom the equation for photosynthesis, we can also determine the limiting factors affecting the r_______ of glucose production in green leaves. The rate of photosynthesis speeds up as light intensity increases, but only up to a point. The overall rate may also be limited by the concentration of carbon dioxide, the temperature or even the colour of light. Factors that can affect the rate of photosynthesis are called limiting factors.

Limiting factors:

6CO2 + 6H20 C6H12O6 + 6O2

Carbon dioxide water light and chlorophyll Glucose Oxygen


Word bank: rate

Light intensity Temperature CO2 Concentration Colour of light

Diagram

Equation

Notes Light from the sun is used to provide the energy required to combine H2O and CO2 during photosynthesis.

The higher the temperature the more often H2O and CO2 molecules collide into each other.

The greater the concentration of CO2 the greater the rate of photosynthesis in green plants.

Red and blue light are absorbed by plants, whereas green light is reflected and not used during photosynthesis.

Limiting factorsLimiting factors light intensity light intensity oneone

During photosynthesis, molecules of water and carbon dioxide collide, form new chemical bonds producing glucose and oxygen. The energy required to form these new bonds in glucose is provided by light energy. The rate of p____________ increases when the amount of light energy increases, but only up to a point. Other factors, like carbon dioxide concentration and temperature also affect the overall rate of photosynthesis. These are called limiting f__________. The factor in shortest supply will always be the limiting factor.

Affect of light intensity on the rate of photosynthesis:Time (seconds)

Oxygen bubbles at 0.1m



30 23 11 3

60 45 22 7

90 67 32 12

120 109 45 17

150 134 65 22

180 157 76 27

210 189 88 32

240 210 109 37

270 245 123 42

300 269 134 45

0.1m 0.2m 0.3m


Word bank: photosynthesis factors

1: Plot a graph of distance (m) versus rate of oxygen production ?2: Is there a relationship between light intensity and rate of photosynthesis ?3: What is this relationship ?4: What are the other limiting factors in this experiment ?5: How could you test out you answer for question 4 ?6: Why is important to control the temperature of the water ?

Experiment 1 2 3

Distance (m) 0.1m 0.2m 0.3m

Diagram

Closed Open Closed

Limiting factorsLimiting factors light intensity light intensity twotwo

During the night, no photosynthesis takes place, just plant respiration. At dusk and dawn when the light intensity is low, the rate of respiration and photosynthesis are roughly the same. During the day, when there is greatest l______ energy, there is a net production of glucose and oxygen. The stomata cells, found on the underside of the leaf open during daylight hours when photosynthesis occurs and partially close during the night. Stomata are opened and closed by the guard cells changing shape. These guard cells contain chloroplasts, which provide the energy for stomata opening and closing.

Affect of light intensity on stomata opening and closing:


Word bank: light

0 2 4 6 8 10 12 14

Bo

dy t

em

pM

icro

be

normal 37oC

time days12am 8 am 12pm 8pm 12am

Ox

yg

en

CO

2U

seG

luco

se

Night Dawn Daylight

time hrs

Dusk Night

0 2 4 6 8 10 12 14

Bo

dy t

em

pM

icro

be

normal 37oC

time days12am 8 am 12pm 8pm 12am

Ox

yg

en

CO

2U

seG

luco

se

Night Dawn Daylight

time hrs

Dusk NightDiagram

Notes

Experiment 1 2 3

CO2 (%) 0.1% 0.25% 0.5%

Diagram

Limiting factorsLimiting factors COCO22 concentration concentration

Time

(seconds)

Oxygen bubbles at 0.1% CO2



30 19 31 43

60 38 54 65

90 68 101 134

120 102 167 201

150 140 223 256

180 180 324 378

210 230 430 498

240 256 489 578

270 298 545 645

300 323 595 702

The rate of photosynthesis increases when the concentration of carbon dioxide increases, but only up to a point. Other factors, like l______ intensity and temperature also affect the overall rate of photosynthesis in green plants. These are called limiting factors. The factor in shortest supply will always be the limiting factor.

Affect of CO2 concentration on the rate of photosynthesis:

0.1% CO2 0.25% CO2 0.5% CO2

0.1m 0.1m 0.1m


Word bank: light

1 :Plot a graph of CO2 concentration (%) versus rate of oxygen production ?

2: Is there a relationship between CO2 (%) concentration and the rate of

photosynthesis ?3: What is this relationship ?4: What are the other limiting factors for this experiment ?

Experiment 1 2 3

Temp (oC) 25oC 35oC 45oC

Diagram

Limiting factorsLimiting factors temperaturetemperature

Time (seconds)

Oxygen bubbles at

25oC

Oxygen bubbles at

35oC

Oxygen bubbles at

45oC

30 19 38 2

60 38 70 3

90 68 128 4

120 102 189 7

150 140 287 11

180 180 356 15

210 230 456 19

240 256 502 22

270 298 615 25

300 323 689 32

25oC 35oC 45oC

0.1m 0.1m 0.1m

The rate of photosynthesis in green plants increases when temperature is increased, but only up to a point, due to other limiting factors like carbon dioxide concentration and light intensity. This is because the two substrates; water and carbon dioxide have a higher kinetic energy, therefore colliding more often and with greater f_______ inside the palisade cell chloroplasts. Very high temperatures stop photosynthesis altogether. This is because, like other enzyme catalysed processes, plant enzymes are denatured when subjected to very high temperatures.

Affect of temperature on the rate of photosynthesis:


Word bank: force

1: Plot a graph of temperature (oC) versus rate of oxygen production ?2: Is there a relationship between temperature and rate of photosynthesis ?3: What is this relationship ?4: What are the other limiting factors ?5: Why, when the temperature was increased to 45oC in expt 3, was the rate of photosynthesis very low ?

Limiting factorsLimiting factors colourcolour of light of light

The rate of photosynthesis can also be affected by the colour of light. This is because green chlorophyll absorbs r____ and b_____ light and reflects green. When green light is reflected, the light energy is not available to the chloroplasts during the formation of g__________ and oxygen from carbon dioxide and water. Why are many of the seaweeds found deep below the water’s surface red ?

Affect of light colour on the rate of photosynthesis: Time (seconds)

White light at 25oC

Blue light at 25oC

Green light at 25oC

Red light at 25oC

30 19 10 4 5

60 38 20 6 11

90 68 34 10 24

120 102 49 12 35

150 140 67 16 48

180 180 100 19 60

210 230 120 24 89

240 256 130 30 99

270 298 140 35 123

300 323 159 42 134

Green RedBlueWhite


Word bank: red blue glucose

1: Plot a graph of colour of light versus rate of oxygen production ?2: Is there a relationship between colour of light and rate of photosynthesis ?3: What is this relationship ?4: What are the other limiting factors ?5: Why is the rate of photosynthesis not zero for green light ?6: Show in a diagram using a green plant leaf, what colours are absorbed and reflected during photosynthesis ?

Expt. 1 2 3 4

Colour of light

White Blue Green Red

Diagram

Plant use of glucosePlant use of glucose general overviewgeneral overview

During photosynthesis in green plants, only glucose (C6H12O6) is manufactured. This glucose is then used by green plants for a number of uses including respiration, fruit production, g________ and repair. Plants are able to take a simple molecule like glucose and manufacture all the other types of molecules, including enzymes, l________, proteins and carbohydrates. They really are food factories and essential to all other animal life. Why is the word producers a good term to use when describing plants ?

Affect of light intensity on the rate of photosynthesis:

C6H12O6

6O2 6CO2

6H2O

Cells

Mitochondria Energy

C6H12O6

6O2 6CO2

6H2O

Cells

Mitochondria Energy

C6H12O6

6O26CO2

6H2O

Cells

ChloroplastLight energy

C6H12O6

6O26CO2

6H2O

Cells


Photosynthesis

Respiration

Growth & reproductionAssimilation

Light energy Respiration

C6H12O6

6O2 6CO2

6H2O

Cells

Mitochondria Energy

C6H12O6

6O2 6CO2

6H2O

Cells

Mitochondria Energy

C6H12O6

6O26CO2

6H2O

Cells


C6H12O6

6O26CO2

6H2O

Cells


Photosynthesis

Respiration

Growth & reproductionAssimilation

Light energy Respiration


Word bank: growth lipids

Diagram

Notes During the day there is a net production of glucose and oxygen by plants as the result of photosynthesis. This glucose is then used during respiration or assimilated and used in the manufacture all the other molecules like proteins, carbohydrates and lipids.

Pollination is the transfer of pollen, the male sex cells from the a_________ of the stamen by b____ or insects to the surface of the female c_________. Once the pollen sex cells have landed on the female carpel, pollination has been achieved. Flowering plants contain both female and male reproductive organs and can either self or cross pollinate. Following fertilisation, where the ovule and pollen cell fuse, the seed begins to develop surrounded by the swollen ovule which forms the f_______. It is the function of the fruit to disperse the seed. What is this organ’s role in the plant life cycle ?

Plant reproductive system:

Plant use of glucosePlant use of glucose reproductionreproduction Science Interactive LTD Copyright 2005

Word bank: anther bees carpel fruit

Pollen cells Female carpel Male anther Reproductive system

Diagram

Notes Pollen, the male sex cells contain the paternal genes and are held on the anther which is part of the male stamen.

The egg cells or ovules contain the maternal genes and are held in the ovule, part of the female carpel.

The stamen is the plant male reproductive organ which contains many millions of microscopic pollen cells.

Flowering plants have both male and female reproductive organs. Plants can self or cross pollinate.

Plant use of glucosePlant use of glucose fruits and tubersfruits and tubers It is the function of the fruit to disperse the seed. Fleshy fruits like apples, pears, oranges and tomatoes contain lots of sugar as a reward for a_________ and insects. These animals and insects, by eating fruit containing seeds, help spread the seeds prior to g_____________ during the following spring. Also roots tubers swollen with carbohydrates, like those found in carrots, turnips and potatoes act as a food reserve for new growth in the following spring. The sugar or carbohydrates contained in the fruit or root tubers is made during photosynthesis and is transported by the phloem tubes from the leaf.

Plant fruits and tubers:Apples Oranges Potatoes Carrots

Diagram

Notes Fruits, root vegetables and nuts all contain sugar or carbohydrates made from sugar produced during photosynthesis. These plant products all contain stored chemical energy which animals then eat, digest and assimilated into their own bodies. Without plants, there would be no food chains and no oxygen, another product of photosynthesis.


Word bank: animals germination

Tropisms in plantsTropisms in plants oneone

Plants can respond to environmental stimuli like light, gravity and water. Unlike humans and other animals, plants cannot move themselves because they lack a skeletal m________ system. Plants can, however grow towards or away from a light source. Plant shoots grow towards the light, whereas plant roots grow towards gravity and moisture. If you germinated a seed in space with zero gravity, what would the growth response of the root be like ?


Auxin accumulates on the dark side of the shoot causing cell elongation and the subsequent bending of the shoot towards the light source


Word bank: muscle

Growing towards the light Response to light in plant shoots

In the picture above, the tree clearly grows towards the primary source of light. Plants respond to light by using a hormone called auxin. Auxin causes cell elongation and is broken down by sun light. The non-illuminated side therefore elongates bending the shoot towards the sunlight. If the sun is overhead, the shoot continues to grow in an upwards direction. Why do we germinate seeds in the dark ?

Tropisms in plantsTropisms in plants twotwo

Plants must grow in one direction or another to respond to stimuli like light, moisture or even gravity. They can’t simply m_______ because thy don’t have a nervous or muscle system. The following experiments help us understand the role auxin plays in controlling a plant’s response. Look at the three different scenarios and predict where auxin is found and how this affects plant growth ?


Scenario one Scenario two Scenario three

Diagram

Notes The shoot responds to the light by growing towards the light. Auxin is found on the dark side (right hand side) and causes cell elongation.

The tip of the shoot is covered with foil. Auxin is present on both sides and in equal amounts. The shoot continues to grow upwards.

The bottom of the shoot is covered. The tip of the shoot where auxin is found is still able to respond to the light stimulus, by growing towards it.


Word bank: move

1: Define the following terms: Photosynthesis, Substrates, Products, Glucose, Oxygen, Limiting factors & Rate-limiting-factors.

2: Look at the diagram of the three types of leaf tissue. Complete the table.

3: Answer the following:

a) How does water and carbon dioxide arrive at the palisade cell for photosynthesis.

b) How is sugar transported around the plant.

c) Sugar is also used by all plant cells during respiration to produce energy for life processes in the plant. Compare photosynthesis and respiration.

d) During the day do plants respire.

e) How could you prove your answers in part (c) by performing an experiment. Explain all the steps.

f) Explain why the leaf cuticle is transparent. What other role does the cuticle play.

Extension questions and homework

Tissue Function the in the green leaf How is it specialised

Stomata

Xylem

Palisade cells

Xylem tubes Palisade cellsStomata


4: Look at the information in the table below. It shows the diameter of the stomata cells over a 24hr period:

a) Explain why the diameter changes over this 24 hr period

b) At midday the light intensity is strongest. How do the stomata cells react to this.

c) At dawn and dusk, is the rate of respiration and photosynthesis the same.

5: a) Other than water and carbon dioxide, plants also need minerals (e.g. phosphates, nitrates and potassium) what are these minerals used for and how do the plants obtain them.

b) Show how a specialised root hair cell takes in minerals like nitrates from the soil.

c) Do the minerals given in part (a) give any energy value to the plant.

d) Compare those minerals that plants require for healthy growth to the minerals and vitamins we require in our own diet.

e) Somebody observed that wheat grows taller and gives a higher yield when the field is closer to a coal burning power station. Suggest a reason for this.

f) Explain why grass doesn’t need cutting during the winter months when the average daily temperature is below 6oC.

6: Complete the following:Plants produce ____________ and oxygen during photosynthesis. This all takes place in the chloroplast found in the _______________ cells. The active chemical in the chloroplast is called _____________. It is able to use light energy to form new chemical bonds between water and carbon dioxide.

Time (hr) 00.00 06.00 08.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00

Diameter (cm) 0.01 0.1 0.15 0.25 0.40 0.40 0.25 0.20 0.10 0.01


7: a) Plants and crops need mineral salts for healthy growth. Give the name of three of these mineral salts.

b) A farmer wants to increase his crop yield by using fertilisers. The able below shows how mass of crop produced from a field depends on the quantity of nitrogen used.

(i) What is the maximum mass of crop that could be produced using nitrogen fertilisers.

(ii) Explain why using 700kg/hectare of fertilisers actually decreases crop yield compared to your answer in part (i).

(iii) Large amounts of fertilisers dissolve in water. When it rains fertilisers can accumulate in rivers and ponds. Explain why this is a problem.

(iv) Some consumers prefer organically grown crops. State two advantages and disadvantages of eating organically grown crops.

8: a) Explain the difference between ‘peat culture’ and ‘nutrient film’ hydroponics.

b) What are the benefits of intensive farming to the (i) farmer and (ii) consumer.

c) What are the disadvantages of intensive farming to (i) the consumer (ii) biodiversity (iii) the environment.

9: Complete the following:

Water passes into the root hair cell by ___________. Mineral salts like _____________ potassium and phosphate are taken up by active transport. A root hair cell has a ____________ surface area to help water and mineral salt uptake. Water is then transported through the ___________ tubes by capillary action to the leaf tissue. Palisade cells require water during photosynthesis to manufacture glucose. Water is lost through the leaves thorough the _____________. They are opened during the day and close at night when no p______________ takes place.

Amount of nitrogen (kg) 0 100 200 300 400 500 600 700

Crop yield (tonnes/hectare)

6 7.5 12 14 15.5 16 15 13

Internet: Go to google.co.uk and find out about fertilizers and how they provide essential minerals for healthy plant growth. Look at how the fertilizers are rated (N:P:K value) and what role each mineral plays in healthy plant growth.


unit 9 photosynthesis in green plants science interactive ltd copyright 2005

Documents

products of photosynthesis

plant leaf system

leaf palisade tissue

overall rate of photosynthesis

similar cells

collection of cells

specialised cells

typical plant