2e: Nutrition (Flowering plants)

photosynthesis

the process of making glucose from sunlight in the leaves of the plant in which light energy is converted into chemical energy

is photosynthesis endothermic or exothermic?

endothermic

word equation for photosynthesis

carbon dioxide + water --> glucose + oxygen

balanced chemical equation for photosynthesis

6CO2 + 6H2O → C6H12O6 + 6O2

factors affecting photosynthesis

- temperature
- light intensity
- carbon dioxide concentration

temperature

increase in temperature = increase in rate of photosynthesis
(since photosynthesis is enzyme-controlled, once it passes the maximum optimal temperature, the enzyme begins to denature and the rate of reaction decreases)

light intensity

- higher light intensity = increased rate of photosynthesis
- increased distance between light source and plant =decreased light intensity

carbon dioxide concentration

increase in carbon dioxide = increase in rate of photosynthesis

parts of a leaf

waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll. lower epidermis, guard cell, stomata

waxy cuticle

- helps reduce water loss by evaporation
- protective layer at the top of the leaf

upper epidermis

thin and transparent to let light into palisade mesophyll

palisade mesophyll

contains chloroplasts for photosynthesis

spongy mesophyll

lots of air spaces for fast gas diffusion (increases surface area to volume ratio)

lower epidermis

contains guard cells and stomata

guard cell

- kidney shaped cells that open and close stomata by absorbing or losing water
- when lots of water is available, the cells fill and open stomata

stomata

- where gas exchange and loss of water by evaporation takes place
- opens during day and closes at night

mineral ions

magnesium, nitrate

magnesium

- required for chlorophyll production
- deficiency: yellowed leaves

nitrate

- required to produce amino acids
- deficiency: stunted growth and yellowed leaves

investigating photosynthesis - practicals

- evolution of oxygen
- carbon dioxide and photosynthesis
- chlorophyll and photosynthesis

evolution of oxygen

oxygen is released as photosynthesis occurs which can be seen as bubbles leave the pondweed

evolution of oxygen - apparatus

- beaker
- water plant
- funnel
- boiling tube
- splint
- bunsen burner
- heat proof mat

evolution of oxygen - method

- submerge a bundle of shoots of a water plant into a beaker of water underneath an upturned funnel
- place a boiling tube with water over the end of the funnel
- bubbles of gas collect in the boiling tube as oxygen is produced

evolution of oxygen - results

show that the gas collected is oxygen by relighting a glowing splint

light and photosynthesis

checking which parts of the leaf are photosynthesising by testing a leaf for starch

light and photosynthesis - apparatus

- beakers
- leaf tissue
- bunsen burner
- tripod
- gauze platform
- prongs
- ethanol
- apron
- safety goggles
- gloves
- iodine solution
- white tile

light and photosynthesis - method (destarching)

- destarch the plant by placing it in a dark cupboard
- partially cover a leaf of the plant with aluminium foil and place it in sunlight
- remove the covered leaf and test for starch using iodine

light and photosynthesis - method (testing for starch)

- drop the leaf into boiling water to kill tissue and break down cell walls
- transfer into hot ethanol in a boiling tube for 5-10 mins to remove chlorophyll
- dip it into boiling water to soften leaf tissue
- spread leaf onto a white tile and cover with iodine solution

light and photosynthesis - results

- green leaf: entire leaf turns blue-black
- area covered with foil: remains orange-brown

light and photosynthesis - analysis

light is necessary for photosynthesis and starch production

light and photosynthesis - safety precautions

- using a water bath
- ethanol is flammable

light and photosynthesis - CORMMS

C - light
O - leaf plant
R - repeat for reliability
M1 - colour change
M2 - 1 day
S - controlled temperature

carbon dioxide and photosynthesis

investigate requirement for carbon dioxide using test for starch

carbon dioxide and photosynthesis - apparatus

- potassium hydroxide solution
- clamps
- conical flasks
- clamp stands
- plant
- beakers
- bunsen burner
- tripod
- gauze platform
- prongs
- ethanol
- apron
- safety goggles
- gloves
- iodine solution
- white tile

carbon dioxide and photosynthesis - method

- destarch the plant
- enclose 1 leaf in a conical flask with potassium hydroxide
- enclose another leaf in a conical flask with no potassium hydroxide (control)
- place plant in bright light
- test both leaves for starch using iodine

carbon dioxide and photosynthesis - why do we use potassium hydroxide

to absorb carbon dioxide from the surrounding air

carbon dioxide and photosynthesis - results

- leaf from conical flask containing potassium hydroxide remains orange-brown
- leaf from conical flask without potassium hydroxide turns blue-black

carbon dioxide and photosynthesis - CORMMS

C - carbon dioxide
O - leaf plant
R - repeat for reliability
M1 - colour change
M2 - 1 day
S - control temperature and light intensity

chlorophyll and photosynthesis - aim

testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising

chlorophyll and photosynthesis - apparatus

* beakers
* leaf tissue (variegated)
* bunsen burner
* tripod
* gauze platform
* prongs
* ethanol
* apron
* safety goggles
* gloves
* iodine solution
* white tile

chlorophyll and photosynthesis - method

* drop leaf in boiling water to kill the tissue and break down cell walls
* transfer leaf into hot ethanol in a boiling tube for 5-10 minutes to remove the chlorophyll so colour changes from iodine can be seen more clearly
* dip the leaf in boiling water to soften the leaf tissue after being in ethanol
* spread the leaf out on a white tile and cover it with iodine solution

chlorophyll and photosynthesis - safety precautions

* bunsen burner should be turned off - ethanol is extremely flammable
* open flame - heat the ethanol is in an electric water bath

chlorophyll and photosynthesis - CORMMS

* C - presence of chlorophyll
* O - leaves will be taken from the same plant or same species, age and size of the plant
* R - repeat for reliability
* M1 - observe the colour change of the leaf
* M2 - 1 day
* S - temperature of the room and light intensity