Plants - Leaves Flashcards
Structure of leaf:
-Epidermis: outer layer of cells. Above leaf = upper epidermis
Below leaf = lower “ “
- Cuticle: Waxy material that covers epidermis
Reduces water loss by evaporation
Barrier against microbes
- Stomaterone: pores - more in lower epi
Allows CO2 into cell for P.S
O2/water diffuse out
- Guard cells: surrounds opening of stomata. Can open or close stomata
- mesophyll: “middle of cell”. 2 layers of P.S cells: Spongy layer- layer of cells which contain air spaces. Less amount of P.S takes place here. Site of gaseous exchange
Palaside layer - layer of cells that contains most chlorophyll. Most P.S takes place here
Factors affecting P.S
- CO2 conc: rate of P.S inc steadily as C02 inc (initially)
After while, rate of P.S doesnt inc despite CO2 inc. A graph would plateaus as CO2 has no effect and therefore no longer a limiting factor
- Temp: Rate of P.S inc steadily as temp rises. Highest rate achieved at opt temp. Higher temp = denaturing emzymes > leads to dec in rate of P.S
- Light intensity: Same as CO2 conc
Plant nutrients.
Starch: Stored as carb in plants
-not soluble and is compact. Test using iodine. Blue/black = Pos
Starch synthesis: Starch = chain of glucose. Plant uses P.S to get glucose and therefore starch. Word Equation- Carbon dioxide + water > glucose + oxygen
Chemical Eq- 6CO2 + 6H2O > C6H12O6 + 6O2
Xylem simplified -
- vessel that carries water.
- water absorbed into roots
- travels up stem
- then carried into leaves by veins
- called transpiration stream
- Water leaves xylem and supplies mesophyll cells for photosynthesis
Phloem Simplified
Vessel that carries products of photosynthesis (e.g glucose) to other areas of the plant where photosynthesis can’t take place
Veins contain both xylem and phloem vessels and so can carry both products
Design and experiment format
Mark 1 : independent variable: V that changes
Mark 2: dependent variable. V that depends on independent V
Mark 3: Controlled- any variable that affect the dependent variable
Mark 4: repeat for reliability
Mark 5: Time period (reasonable)
Mark 6: Results- how to collect
Plants gas exchange:
net gas exchange in trees!-
-respiration takes place all the time in trees
- it is necessary for all the cells to be provided with energy for their survival therefore light intensity has no affect on the rate of respiration for trees.
When does P.S take place most?
-P.S is the highest during high light intensity
- does not take place in dark. Net release of O2 in the day whilst net intake of C02 at night
The Stomata:
- Stomata are surrounded by guard cells
- these guard cells open in light
- Allows CO2 to the diffuse in and O2 out
- in dark the guard cells close
- this is useful as photosynthesis cannot take place at night due to lack of sunlight
The Phloem pt.2
-transport tissue found in plants
-cells are arranged end to end
Cell walls made out of Celulose- have holes called sieve plater
these holes allow for cytoplasm from cell to extend to other cells
- since cytoplasms are on now connected, the plates form a sieve tube- transports products of P.S such as sucrose and amino acid’s from the leaves to other parts of the plant
- sieve tubes does not contain nuclei. companion cell is responsible for control
Xylem pt.2
- The xylem is responsible for movement of water and minerals from the roots to other parts of the plant
-it is made out of dead cells that are connected from one end to another
- vessels do not cytoplasm but have a central space called lumen
Water travels up the lumen to Leaves for photosynthesis
Transpiration:
- after travelling up the xylem the water reaches the Mesophyll cells in the leaves
- lots of water because at the surface of the leaf by evaporation. This is called transpiration
- transpiration stream uses: - provides water for P.S./ carries ions dissolved in water/ provides water which keeps plant cells turgid/ evaporation from leaf can cool the surface of the plant
How do guards cells open?:
- contains chloroplasts - Allows P.S to take place
- Energy stored can now be used to accumulate -Solutes with in Guard cells
- this reduces water potential in Guard cells > water travels along the water potential gradient by osmosis > Guard cells become turgid and stomata open transpiration can take place
Measuring rate of transpiration Potometers:
- Potometer: measures rate of transpiration or rate of uptake of water by plant
Weight Potometer: - measures loss of weight from potted plants or leaves shoot over a long period of time
-Polyphene bag prevents evaporation of moisture from soil
-most mass lost due to water oppression from leaves during transpiration
Volume Potometer:
- finds water uptake by leafy root
- simplest is straight vertical tubes joints to shoot by rubber tuning
- Set up = put plants in sink of water and any in tubing is removed > shoot taken and cut at angle > removed from sink and Vasoline used to join seal > movement of water in the Tube can be timed> water moving quickly = faster rate of transpiration
Factors affecting transpiration
Light intensity - increased rate because stomata is open
Temp - higher temperature increases rate as rate of evaporation of water from mesophyll cells is increasing
Humidity - rate decreased when humidity increases because diffusion gradient is reduced
Wind speed - faster and movement = faster rate of transpiration
Root hair cells:
- tiny specialised cell found in roots
- responsible for absorption of water
- Teynes high concentration of mineral salts compares to soil > as Lower potential than soil > lead to osmosis > water enters root hair cell which leads to dilation of cell content > water potential now higher in root hair cells > consequently water will travel from root hair cells to cortex and up the xylem due to water potential gradient
Uptake of mineral ions:
- Ions needed to make range of organic compounds from products of P.S
- taken from soil with water via osmosis (only water uses Osmosis)
- just ends up root cells by other way:
- Active transport: some mineral ions use this depending on concentration of soil > once inside the route they pass along the cortex by mainly diffusion and enter xylem vessels > carried around plants in transpiration stream
Mineral ions necessary for plant growth:
- Nitrates: required for amino acid’s proteins and chlorophyll and DNA. Is absorbed from Soil water
- Magnesium: forms a part of chlorophyll molecule
- Potassium: required for respiration and photosynthesis
Phosphate- insure for DNA and is part of the cell membrane
Deficiency of Ions:
- Nitrates: stunted growth and leaves Can turn yellow
- Magnesium: leaves turn yellow as chropyll not present
- Potassium: leaves turn yellow and have dead spots
- Phosphates: Poor growth
