1.2 Photosynthesis

Photosynthesis

Photosynthesis

process to create glucose from carbon dioxide and water, using light energy from the sun

Glucose

C₆H₁₂O₆

Insoluble starch

complex carbohydrate made from products of photosynthesis and used for storage

Chloroplast

organelle where photosynthesis occurs

Chlorophyll

green pigment that absorbs light energy used to carry out photosynthesis

Light intensity effect

Photosynthesis rate increases as more energy is available, up to a certain point

Carbon dioxide concentration effect

Photosynthesis rate increases as more carbon is available, up to a certain point

Photosynthetic rate

speed which plants take in reactants to produce products

Testing leaves for starch

Plant leaves can be tested for the presence of starch using iodine solution, after the leaf has been intensely heated and submerged in ethanol

Iodine test for starch

change colour from orange to blue-black

Starch results for plants kept in light conditions

Plants store glucose as starch in the leaves, plants that are kept in the light will photosynthesise and store starch so their leaves will change colour to blue-black

Starch results for plants kept in the dark

Plants in the dark will be unable to photosynthesise meaning glucose will not be made and stored as starch, so iodine will not change colour

Starch results for variegated leaves

Leaves that are variegated have patches absent of chlorophyll, these regions will not cause iodine to change colour as photosynthesis cannot occur here

Investigating photosynthesis in pondweed

Aquatic plants produce observable bubbles of oxygen when photosynthesising near light

Pondweed bubbles

presence of oxygen from photosynthesis, more bubbles =greater rate

Light intensity and rate of photosynthesis in pondweed

closer=greater light intensity=increase the rate of photosynthesis

Sodium hydroxide

A basic solution that can break down carbon dioixde

Effect of plant kept enclosed near sodium hydroxide

a sealed bag with sodium hydroxide will be unable to photosynthesise due to a lack of carbon dioxide

Photosynthesis

A process where plants and algae synthesise glucose from carbon dioxide and water, using light energy from the sun

Photosynthesis word equation

Carbon dioxide + water (light energy+chlorophyll) -> glucose + oxygen

Balanced equation for photosynthesis

6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂

Oxygen

6O₂

Carbon dioxide

6CO₂

Water

6H₂O

Endothermic reaction

energy is taken in from surrounding environment

Temperature effect

Photosynthesis rate increases to an optimum and then decreases due to denaturing enzymes

Light intensity effect

Photosynthesis rate increases as more energy is available, up to a certain point

Carbon dioxide concentration effect

rate increases as more is available up to a certain point

Cellulose

Carbohydrate component of plant cell walls made from products of photosynthesis

Amino acids

Building blocks of protein made from products of photosynthesis

Enzymes

should be maintained in optimal conditions for efficient rates of photosynthesis

Adding a leaf to boiling water during a starch test

Kills the leaf to prevent any further reactions that might break down starch or affect its presence

Adding hot ethanol during a starch test

remove chlorophyll from the leaf

Washing the leaf before examination during a starch test

Softens the leaf

Risk of starch tests

using bunsen burners, ethanol is very flammable and should be kept away from flames

Dependent variable

The variable that is measured, in this case the presence of starch or colour of iodine test

Independent variable

The variable that is changed such as the type or source of leaf

Control variables

The variables that are kept the same

Temperature

Increases the rate of reaction up to an optimum rate, after which the denaturation of enzymes will occur

Sunlight

Is needed as an energy source for photosynthesis to occur

Carbon dioxide

Enters the plant through stomata is the source of carbon needed to make glucose

Temperature effect

Photosynthesis rate increases to an optimum and then decreases due to denaturing enzymes

Light intensity effect

Photosynthesis rate increases and then plateaus due to another limiting factor such as temperature or carbon dioxide

Carbon dioxide concentration effect

Photosynthesis rate increases and then plateaus due to another limiting factor such as temperature or light intensity

Limiting factor

An environmental factor that prevents photosynthetic rate from increasing

Three main limiting factors

Temperature, light intensity and carbon dioxide concentration

Plateau

Where a graph levels off and no longer increases past a certain point

Inverse-square law

Light intensity is inversely proportional to the square of the distance from a light source

Inversely proportional relationship

As the distance of light from a plant increases, the light intensity decreases

Purpose of photosynthesis

products used for respiration and to make new molecules

Purpose of respiration

to obtain energy, used for growth, new molecules, movement in animals, and temperature regulation

Aerobic respiration

take in glucose from food and oxygen from the air to release energy, products released into the air

When photosynthesis occurs

In light conditions during the day, assuming conditions are available

When respiration occurs

All the time in animals and plants, plant respiration is more observable at night as they do not photosynthesise at this time

Gas exchange

swapping of gases, can occur in the stomata or the lungs

Hydrogencarbonate indicator

detect increases and decreases of carbon dioxide concentration, to interpret the effect of gas exchange

Hydrogencarbonate indicator colour changes

normally red, will change to purple in low concentrations and yellow in high

In light conditions

rate of photosynthesis is higher than respiration, net gas exchange oxygen out

Hydrogencarbonate indicator result for light conditions

purple

At dusk or dawn

light intensity is low the rates of photosynthesis and respiration are equal, known as the compensation point with no net gas exchange, CO₂ 0.03%

Hydrogencarbonate indicator result for low light conditions (dusk/dawn)

will be red because no carbon dioxide change will be detected, compensation point has been achieved where respiration occurs at the same rate as photosynthesis

In dark conditions

Only respiration is occurring as there is no light for photosynthesis

Hydrogencarbonate indicator result for dark conditions

turns to yellow as rate of photosynthesis is lower than the rate of respiration

Mesophytic leaf

adapted to general conditions, those that are not too dry or too humid

Epidermal tissue

covers and protects the plant, physical defence, transparent to allow light through

Waxy cuticle

protect plant and reduce water loss, thicker on upper surface, transparent

Palisade mesophyll

below epidermis, compacted together and contain high quantities of chloroplasts

Spongy mesophyll

Layer of tissue beneath palisade mesophyll, packed loosely for efficient gas exchange with increased surface areas

Intercellular space

space between to provide room for increased rate of diffusion

Stomata

Small openings on the underside of a leaf

Role of the stomata

opens to allow gas exchange

Guard cells

Pairs of cells that surround the stomata and control their opening and closing to optimise gas exchange and reduce water loss

Activity of guard cells

open stomata in light conditions and close at night

Xylem

Non-living vascular tissue that carries water and dissolved minerals from the roots of a plant to its leaves, the xylem is hollow and nearby cells are lignified or dead so water can move continuously

Phloem

Living and elongated vascular tissue that carries sugar and organic substances throughout a plant, the phloem has sieve plates that act as pores to allow molecules to diffuse between cells