Plants

plants

What is photosynthesis?

a metabolic reaction occurring in plants where light energy converts raw materials into carbohydrates- glucose

what is the word equation for photosynthesis?

carbon dioxide + water ---(with light energy)---> glucose + oxygen

Balanced chemical symbol equation for photosynthesis

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

How does varying carbon dioxide concentration affect rate of photosynthesis?

Increasing carbon dioxide concentration increases rate of photosynthesis

until above a certain threshold, further increases in carbon dioxide concentration do not increase rate of photosynthesis—> another factor (such as light intensity) is limiting rate of reaction at which the rate plateaus

How does varying light intensity affect rate of photosynthesis?

Increasing light intensity increases rate of photosynthesis

until above a certain point where it doesn’t increase rate of photosynthesis—> another factor (such as CO2 or temperature) is limiting rate of reaction at which the rate plateaus

How does varying temperature affect the rate of photosynthesis?

Low temperature:

Rate is low because enzymes have less kinetic energy, —> fewer collisions with substrates.

Optimum temperature (~40 °C):

Rate is highest because enzymes have enough kinetic energy to work at most efficient rate.

High temperature:

Rate decreases sharply because enzymes denature—> active site changes shape so substrates cannot bind

What is the structure of a leaf made of?

waxy cuticle

upper epidermis

palisade mesophyll

spongy mesophyll

lower epidermis

stomata + guard cells

vascular bundles (xylem and phloem)

function and adaptation of waxy cuticle

Protective layer on upper and lower sides of the leaf, prevents water loss

function and adaptation of upper epidermis

Thin and transparent to allow light to enter palisade mesophyll layer underneath it

function and adaptation of palisade mesophyll

Column-shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis

function of lower epidermis

Contains guard cells and stomata

function and adaptation of stomata

Where gas exchange takes place: opens during the day, closes during the night

In most plants, more stomata are found on the underside of the leaf to reduce water loss

function and adaptation of guard cells

Absorbs and loses water to open and close the stomata

function and adaptation of vascular bundle (xylem and phloem)

xylem- transport water and dissolved minerals

phloem- Transports sucrose and amino acids

function and adaptation of spongy mesophyll

Contains internal air spaces that increase the SA:V ratio for the diffusion of gases

what mineral ions do plants require?

magnesium

nitrate

why do plants need magnesium ions?

needed to make chlorophyll

why do plants need nitrate ions?

make amino acids

why is oxygen produced in the pondweed (elodea) experiment?

because oxygen is a product of photosynthesis

why is light needed in the pondweed (elodea) experiment?

to make the chemical energy needed to create carbohydrates

—>increasing the light intensity will boost the speed of photosynthesis

describe production of starch test on a leaf

Keep plants in dark for 24-48 hours

Kill the leaf with hot water bath

Remove chlorophyll using ethanol

Rinse leaf and add iodine

Blue-black colour = starch present

Orange-brown = starch not present

why does starch show photosynthesis has occured?

Starch is a product of photosynthesis

Light-exposed leaf areas turn blue-black (starch present)

Covered areas stay yellow-brown (no photosynthesis)

Shows light is needed for photosynthesis and starch production

why is chlorophyll removed in the starch test on a leaf?

because it’s green and would mask blue-black colour change that shows presence of starch when iodine is added

removing chlorophyll makes leaf colourless, so it’s easier to see where starch has been produced

compare the rate of photosynthesis and respiration during daylight

photosynthesis rate > respiration rate

net carbon dioxide in

net oxygen out

compare the rate of photosynthesis and respiration during darkness

rate of photosynthesis < rate of respiration

only respiration occurs- no sunlight

how is the structure of a leaf adapted for gas exchange?

thin which gives short diffusion distance

flat which provides large SA: V ratio

many stomata which allow movement of gases in and out of air spaces by diffusion

why can simple, unicellular organisms rely on diffusion for movement of substances in and out of the cell?

Small

Large SA:V ratio

One cell thick

Works with diffusion over short distance

—> fast enough to supply nutrients and remove waste products

why can’t multicellular organisms rely on diffusion alone?

Large

Small SA:V ratio

Many cells have high demands

why do multicellular organisms need a transport system?

Moves substances quickly over long distances
Supplies all cells with oxygen and nutrients
Removes waste products e.g, CO2
Maintains concentration gradients, allowing diffusion to continue at cells

Eg of transport system in plants

vascular system- xylem and phloem