B1.4 - Photosynthesis Flashcards
What are the reactants in photosynthesis?
Water and Carbon dioxide
What is the word equation for photosynthesis?
Carbon dioxide + water -> oxygen + glucose
State the balanced chemical equation for photosynthesis
6CO + 6H O -> 6O + C H O
2 2 2 6 12 6
What happens during photosynthesis?
- Carbon dioxide is absorbed from the air, and water is absorbed from the soil. Energy from the sun is converted to light energy.
- those three substances react together to make glucose
- waste products (ie. oxygen) is released into the atmosphere
where does photosynthesis occur?
in the chloroplasts of plants
why are leaves and stems green?
since they contain chlorophyll
what is the role of chlorophyll in plants?
to absorb light energy from the sun
What are the two main stages of photosynthesis?
and give a brief description of what happens
Stage 1 - Light Dependent
- when energy transferred from light splits water molecules into hydrogen ions and oxygen gas
Stage 2 - Light Independent
- when carbon dioxide gas combines with hydrogen ions to make glucose
what kind of reaction is photosynthesis, and why?
an endothermic reaction (energy is transferred from surroundings to keep it going - ie. energy from sun)
How is glucose produced during photosynthesis used? (6)
- respiration
- converted into sugar molecules and stored in fruit
- starch (food stores used at night - when no sunlight)
- cellulose (cell walls)
- nitrogen = proteins (for growth and repair)
- fats and oils (food store + growth)
HINT - don’t need all uses, only correct idea (not in spec)
Describe how to test a leaf for the presence of starch
- place leaf in beaker of boiling water to kill it + break down the cell walls = iodine absorbed
- place a leaf into a boiling tube of boiling ethanol for 1 minute (to remove chlorophyll in order to see colour change better) using forceps (ensure water bath used to heat ethanol, as flammable)
- then wash it under water to remove the ethanol and to soften it
- place the leaf on a white tile, spread it out, and add a few drops of iodine solution (mixture of iodine and potassium iodide) on it
- if the leaf turns from yellow/brown to black/blue, it contains ethanol
How do you prove that chlorophyll is needed for photosynthesis?
- place a destarched (placing the plant in the dark for a minimum of 24 hours) variegated leaf (ie. has white and green parts) into sunlight for a few hours
- then test for starch by adding a few drops of iodine
- if plant becomes black-blue = starch is present (chlorophyll present there)
- if leaf stays orange = no starch present (no chlorophyll present there)
How do you prove that light is needed for photosynthesis?
- get a destarched leaf and cover half ish with a piece of black card
- place the leaf in sunlight for a few hours
- take the black card off and test for starch
How do you prove that Carbon Dioxide is needed for photosynthesis?
- Place a destarched plant in a sealed plastic bag with a pot of soda lime (which absorbs carbon dioxide)
- place the plant in sunlight for a few hours
- test the leaves for starch
How do you prove that oxygen if given off during photosynthesis?
- place an upside test tube on a beaker of a sea plant
- as the test tube fills up with air/bubbles, put a glowing splint in the test tube
- it will relight if oxygen is present
state three factors which affect the rate of photosynthesis
- temperature
- light intensity
- carbon dioxide concentration
describe the effect of light intensity on the rate of photosynthesis
higher the light intensity, higher the rate of photosynthesis
how does carbon dioxide affect the rate of photosynthesis?
- greater carbon dioxide concentration, faster rate of reaction
how does temperature affect the rate of photosynthesis?
- photosynthesis is an enzyme-controlled reaction
- higher temp, faster reactions
- too high temp, enzyme can denature and reactions stop
Describe one way to measure the rate of photosynthesis
- volume of oxygen given off per minute (by pondweed)
- count the number of bubbles produced per minute
how do you study the effect of light intensity on the rate of photosynthesis?
pace a light source at different distances from pondweed
what is the equation for the relative light intensity?
= 1
————————————
distance from light source^2
how do you study the effect of carbon dioxide concentration on the rate of photosynthesis?
- add different masses of potassium hydrogen carbonate powder to water
- potassium hydrogen carbonate powder releases carbon dioxide into atomsphere
how do you study the effect of temperature relative to the concentration on the rate of photosynthesis?
- place the apparatus in water baths at different temperatures
What is a limiting factor?
When one factor required during photosynthesis is not present, and so the rate of photosynthesis cannot increase
A factor which, if in short supply limits or reduces the rate of photosynthesis, eg temperature, light intensity and carbon dioxide concentration.
Describe the process of photosynthesis
- an endothermic reaction
- use of (sun)light energy
- use of carbon dioxide and water
- produce : glucose / carbohydrate / starch, and oxygen
- use of chlorophyll / occurs in chloroplasts
State what is meant by light intensity
the brightness of light / amount of light that a plant receives during photosynthesis
using what process do root hair cells absorb water?
osmosis
using what process do root hair cells absorb mineral ions?
active transport
What absorbs CO2, and what releases CO2
Soda lime - absorb carbon dioxide and water vapour
Potassium hydrogen carbonate - releases carbon dioxide to the atmosphere
