Topic 3: Leaves Flashcards
Features, functions, photosynthesis.
Describe photosynthesis
the process by
which plants synthesise carbohydrates from raw
materials using energy from light
State the word equation for photosynthesis
carbon dioxide + water → glucose + oxygen
in the presence of light and chlorophyll
What is chlorophyll?
Chlorophyll is the protein found within chloroplasts that catalyses the reaction. It is also what causes plants to be green!
Chlorophyll function?
chlorophyll transfers energy from light
into energy in chemicals, for the synthesis of
carbohydrates
State the balanced chemical equation for
photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
Outline the subsequent use and storage of the
carbohydrates made in photosynthesis,
(a) starch as an energy store
(b) cellulose to build cell walls
(c) glucose used in respiration to provide energy
(d) sucrose for transport in the phloem
(e) nectar to attract insects for pollination
Explain the importance of nitrate ions and magnesium ions
a) nitrate ions for making amino acids, Stunted growth
Leaves (usually near growing tip) start to turn yellow
(b) magnesium ions for making chlorophyll, Yellowing between the veins of leaves (known as chlorosis) due to lack of chlorophyll production
Identify and explain the limiting factors of
photosynthesis in different environmental
conditions
When a process depends on two or more factors (variables), the rate of that process is determined by the factor which is in shortest supply.
The main limiting factors are
Light intensity
Carbon dioxide concentration
Temperature
Leaf features and how these features are adaptions for photosynthesis
most leaves have a large surface area
and are thin - aid diffusion.
Investigate the need for chlorophyll, light
and carbon dioxide for photosynthesis, using
appropriate controls
starch v glucose
Plants make glucose but leaves cannot be tested for its presence as the glucose is quickly used, converted to other substances, transported, or starch.
Starch is in chloroplast where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.
Investigate and describe the effect of light and
dark conditions on gas exchange in an aquatic
plant using hydrogen carbonate indicator solution
DAY V NIGHT
The ratio of photosynthesis to respiration in plants changes over the day cycle
Plants are constantly respiring and releasing carbon dioxide
Plants only photosynthesise during the day when sunlight is available, taking in carbon.
During the day plants photosynthesise faster than they respire, resulting in a net intake of carbon dioxide
During night plants respire more than they photosynthesis, resulting in a net release of carbon dioxide
Hydrogen carbonate indicator is a pH indicator that changes colour depending on the pH of a solution
Carbon dioxide is acidic.
Higher carbon dioxide concentration = more acidic
5 Uses of glucose in plants to remember!
- Glucose is commonly stored in plants as starch (long chains of glucose)
- Glucose can be used in cellulose to build cell walls
- Glucose can be used for respiration
- Glucose can be converted in to sucrose and transported through phloem vessels from source to sink
- Glucose can be converted in to nectar and used to attract pollinators
Parts of the leaf
Guard cells
Waxy Cuticle
Epidermal cells
Palisade mesophyll- chloroplast + vacuole
Spongy mesophyll
Vascular bundle - xylem + phloem
Stomata
Guard cells function
Open and close stomata
Waxy cuticle function
Allows light to pass through whilst protecting leaf surface
Epidermal cells function
offers protection but thin to allow light through
palisade cell function
Contain many chloroplasts
Packed tightly together
Large surface area
Large vacuole pushes chloroplast to edges of cell
Thin cell walls to aid gaseous exchange
ALL OPTIMISED FOR LIGHT EXPOSURE
Spongey mesophyll function
Irregular shaped
Fewer chloroplasts
Smaller than palisade cells
Spaced out with air pockets in between
OPTIMISED FOR ALLOWING GASES TO PASS EASILY
Vascular bundle (xylem and phloem) functions
Xylem - transport of water and mineral ions, and support.
Phloem - transport of sucrose and amino acids
Xylem vessel structure in relation to their function
Thick walls with lignin
No cell contents
Cells joined end to end with no cross walks to form a continuous tube
Root hair cells feature
Root hairs increases surface area, therefore increasing the rate of osmosis / diffusion
Water trip through plant
soil -> root hair cell -> root cortex cells -> xylem -> mesophyll layer -> air pockets -> stomata -> atmosphere
transpiration definition
Transpiration is the loss of water vapor from leaves
How does transpiration affect water concentration in leaf?
Causes water concentration in leaf to decrease
Water moves by osmosis down water potential gradient from soil to xylem vessels then up the plant to the leaves
What causes plants to wilt?
if more water evaporates from a plant than can be absorbed from the soil, the plant cells will become flaccid, causing the plant to wilt
How does cohesion and adhesion allow water to move up xylem vessels?
Cohesion of water and adhesion to the walls of the xylem vessel allows water to move up xylem vessels, like water up a straw
Effects of limiting factors on transpiration
temperature increases the rate until another factor is the limiting factor
humidity decreases the rate of transpiration because it decreases the leaf’s water concentration
Higher wind speed = faster evaporation of water out of stomata = faster rate of transpiration
Describe translocation
the movement of
sucrose and amino acids in phloem from sources
to sinks
What are sources and sinks?
sources as the parts of plants that release
sucrose or amino acids
sinks as the parts of plants that use or store
sucrose or amino acids
Explain why some parts of a plant may act as a
source and a sink at different times
phloem can transport these nutrients in any direction.
carbs in plants: produced by photosynthesis as glucose, transported as sucrose, used for respiration
Concentrations (1, high to 5, low) of CO2 vs hydrogen carbon indicator colour and the condition of the plant. (investigating light)
- yellow
- orange
respiration > photosynthesis, lower pH, more acidic - red
respiration = photosynthesis - magenta
5.purple
respiration < photosynthesis, higher pH, more alkaline
What’s a limiting factor?
A limiting factor is something that is in short supply that restricts a process
Effect of light intensity on photosynthesis.
The rate of photosynthesis increases with light intensity
When the intensity of light increases to a certain point, photosynthesis cannot go any faster.
Effect of carbon dioxide concentration on photosynthesis.
Increasing the CO2 concentration, increases rate of photosynthesis
BUT, there is a maximum rate
Effect of temperature on photosynthesis
Too much heat damage enzymes and causes them to denature
Too much heat also evaporates water out of leaves and forces stomata to close
Too little heat can reduce enzymes reaction rate by reducing number of collisions between the enzyme’s active site and substrate
