12 — nutrition& transportation in plants Flashcards
External features of leaf adapted for photosynthesis
Broad and thin lamina/ leaf blade (p: laminae):
- Increases the sa:v for maximum absorption of light energy
- Shorter diffusion distance for faster diffusion of gases into the leaf, via the stomata
- Enables light energy to reach all mesophyll cells
Network of veins:
- Veins allow transport of water and dissolved mineral salts from the roots to the mesophyll cells via xylem
- transports sucrose and amino acids from the leaves to other parts of the plant via phloem
Petiole:
- Positions lamina away from stem for maximum absorption of light energy and gaseous exchange (carbon dioxide and oxygen).
- Adaptations due to absence of petiole:
- Leaves r longer, broader lamina -> ^SAtVR
- Leaves bend at an angle away from stem
Leaves r usually arranged in a regular pattern around the stem
- ensure that leaves are not blocking one another from sunlight and that each leaf receives optimum amount of light energy
Waxy transparent cuticle structure + function
Waxy and waterproof layer above the epidermis
- Reduce excessive water loss via evaporation.
Transparent
- to allow light energy to penetrate and reach the mesophyll cells.
- Absence of chloroplast
Upper/lower epidermis
- UE: absence of chloroplasts
- LE: presence of chloroplasts in guard cells
- Single layer of closely packed epidermal cells and produce the waxy cuticle
- both protects inner part of leaf from injury
- Upper Epidermal cell is transparent to allow light to penetrate through the leaf to the cells and protect the inner cells from injury; [1]
- LE contain minute openings such as stomata for gaseous exchange (carbon dioxide and oxygen) between the surrounding and the leaf cells.
Palisade mesophyll
Main site of photosynthesis
- Contains chloroplast
- Long and cylindrical, vertically arranged n closely packed-> ^ total amt of light absorbed by chloroplasts
- Contains the most amount of chloroplasts and is found at the top of the leaf
- for maximum absorption of light energy for photosynthesis
Contains numerous/ many chloroplasts where chlorophyll in the chloroplasts absorb light energy and converts it to chemical energy to synthesise glucose during photosynthesis in the presence of carbon dioxide and water; [1]
Spongy mesophyll
- Contains chloroplast
- Irregular shaped cells, more loosely packed
- Has numerous intercellular air spaces
- for rapid diffusion of carbon dioxide, oxygen and water vapour inside the leaf cells
- for water plants, this can provide buoyancy for the leaf to float on water.
- Contain fewer number of chloroplasts than the palisade mesophyll cells
- Has a thin film of moisture on the surface of the spongy mesophyll cells to allow carbon dioxide to dissolve first before diffusing into the cells for photosynthesis to tk place.
- Contains vascular bundle
Intercellular air spaces
- Mesophyll cells coated with thin film of moisture, allowing CO2 to dissolve in it b4 diffusing into mesophyll cells for photosynthesis to tk place
- Hv large SAtVR for CO2 and O2 to quickly diffuse in n out of mesophyll cells
Vascular bundle
Contains
- Xylem – transport water and dissolved mineral salts from the roots to the leaves.
- Phloem – transports sucrose and amino acids from the leaves to other parts of the plant.
Guard cells
- Contains chloroplast that has chlorophyll to allow photosynthesis to occur
- Regulates the opening and closing of the stomata for gaseous exchange between surrounding and the leaf cells
- Forms tiny openings, stomata, that’s usually absent /present in low numbers at upper epidermis: prevent excessive water loss thru evaporation
- Controls size of stomata
- Each stoma surrounded by guard cells
- Cell wall near stoma is thicker
Desc how guard cells control movement of substances in n out of leaf/the general mechanism of stomata opening during the day. [6]
- In presence of light, guard cells photosynthesise to convert light energy to chemical energy [1]
- Forming glucose used to release energy -> pump potassium ions into cells, lowering their WP [1]
- Net movement of water molecules from adjacent epidermal cells into guard cells via osmosis [1]
- Cells turgid n change shape, guard cells become curved n pull open stomata. CO2 enters, O2 n water vapour exits leaf via stomata
- (In absence of light: guard cells close stomata, restricting movement of these gases)
Adaptation for photosynthesis (CSCCIN)
Waxy, transparent cuticle on upper n lower epidermis:
- Reduces excessive water loss through evaporation from the leaf
- Transparent for light energy to penetrate and reach mesophyll cells
Stomata present in epidermal layers
- In presence of light energy, stomata (plural) opens wider to allow carbon dioxide to diffuse in and oxygen, water vapour to diffuse out of the leaf
Chloroplasts in all mesophyll cells contain chlorophyll
- Chlorophyll absorbs and convert light energy to chemical energy for synthesis of glucose during photosynthesis
More chloroplasts found at palisade mesophyll cells compared to spongy mesophyll cells
- found at the top of the leaf for maximum absorption of light energy for photosynthesis
Intercellular air spaces in spongy mesophyll
- Mesophyll cells coated with thin film of moisture, allowing CO2 to dissolve in it b4 diffusing into mesophyll cells for photosynthesis to tk place
- Hv large SAtVR for CO2 and O2 to quickly diffuse in n out of mesophyll cells
Network of veins containing xylem n phloem situated close to mesophyll cells
- - Xylem – transport water and dissolved mineral salts from the roots into the mesophyll cells
- Phloem – transport sucrose and amino acids from the leaves to other parts of the planot
Describe and explain how the leaf is adapted for photosynthesis [6] (Any 6)
- Petiole / leaf stalk to hold leaf in position to absorb maximum light energy [1]
- Thin broad lamina / leaf blade to provide short diffusion distance for gases / enables light to reach all mesophyll cells / increase surface area to volume ratio for maximum absorption of light energy. [1]
- Waxy cuticle to prevent excess water loss / reduces water loss through evaporation from the leaf / transparent for light to enter the leaf. [1]
- Stomata present in epidermal layers/lower epidermis to allow carbon dioxide to diffuse in and oxygen to diffuse out of the leaf. [1]
- Chloroplasts containing chlorophyll to absorb and transforms light energy to chemical energy used In the manufacture of sugars [1]
- More chloroplasts in the upper palisade tissue/in palisade mesophyll cells to absorb more light energy near the leaf surface [1]
- Intercellular air spaces to allow rapid diffusion of carbon dioxide / oxygen into and out of mesophyll cells [1]
- Veins containing xylem and phloem situated near mesophyll cells. Xylem transport water and mineral salts to mesophyll cells. Phloem transport sugars away from the leaf [1]
- Presence of guard cells to regulate / control the opening and closing of stomata for gaseous exchange
- Mesophyll cells lines with thin layer of moisture to allow gases to dissolve
Stoma
- Open in presence of light energy
- Glucose formed during photosynthesis (in guard cells) release Chem energy thru aerobic respiration -> pump potassium ions into guard cells via AT -> conc of potassium ions ^ , decreasing WP of cell sap in guard cells -> net movement of water molecules from adjacent epidermal cells into guard cells via osmosis -> guard cells swell, becomes turgid and curved -> pulls stoma to open wider.
- Allows diffusion of CO2 from atmosphere into leaf thru stomata for photosynthesis to synthesise glucose
- WV diffuses out of leaf thru stomata during transpiration -> transpiration pull in xylem to draw H2O up from roots to stems n leaves for photosynthesis to synthesise glucose for growth.
- Close in dark
- Potassium ions diffuse out of guard cells -> WP of cell sap in guard cells ^ -> net movement of water molecules out of guard cells by osmosis -> guard cells flaccid n stoma closes
- Hot n sunny day:
- Excessive water loss thru evaporation in guard cells -> flaccid, stoma close to prevent further water loss thru evaporation n diffusion
- Gaseous exchange: CO2
- CO2 rapidly used up for photosynthesis -> CO2 conc in leaf lower than atmospheric air -> CO2 diffuses from surrounding air thru stomata into intercellular air spaces down a CG -> dissolve in thin film of water on mesophyll cells -> diffused CO2 diffuses into chloroplasts for photosynthesis
- Water loss:
- There is a network of veins containing xylem and phloem at leaf. Water n dissolved mineral salts transported by xylem from roots to leaf -> move from cell to cell thru mesophyll cells
Describe the process of photosynthesis. [4] + [6]
- Chlorophyll in chloroplast to absorb light energy and convert to chemical energy [1]
- Photolysis of water to form oxygen gas and hydrogen atoms using light energy [1]
- Carbon dioxide diffuse through stomata down the concentration gradient from the environment into the leaf [1]
- Hydrogen atoms and chemical energy from photolysis is used to reduce carbon dioxide is reduced into glucose [1]
[6]:
During the light dependent stage, chlorophyll in chloroplasts in leaves absorbs light energy and converts it into chemical energy; [1]
Light energy is used to split water molecules into oxygen gas and hydrogen atoms/ ions through photolysis of water; [1]
During the light independent stage, hydrogen atoms/ ions, chemical energy and enzymes are used to reduce carbon dioxide to glucose; [1]
Carbon dioxide is obtained through diffusion into the stomata in the leaves and water is obtained from the soil through the roots, up the stem and into the leaves; [1]
Oxygen, a by-product diffuses out of the leaves via the stomata; [1]
The chemical equation for photosynthesis is
6CO2 + 6H2O C6H12O6 + 6O2 ;
Explain photosynthesis.
Light energy is trapped by chlorophyll and converted to chemical energy. Water molecules are split into oxygen and hydrogen atoms through photolysis of water and the oxygen produced is released as a by-product. Enzymes use the hydrogen atoms and chemical energy to convert carbon dioxide into glucose which can be oxidised to release energy in plants, during photosynthesis.
Carbon dioxide + water → glucose + oxygen
(Light energy and chlorophyll)
Outline the pathway of a carbon dioxide molecule from the time it enters the leaf until it eventually becomes part of a glucose molecule in a leaf cell. [6]
- Carbon dioxide diffuses into leaf from environment down concentration gradient [1]
- via the stomata and store in intercellular spaces [1]
- Carbon dioxide dissolve in the film of moisture on the spongy mesophyll cell [1]
- Dissolved carbon dioxide diffuse into the cell and into the chloroplasts. [1]
- Combines with hydrogen ions and chemical energy [1]
- to reduce into glucose during photosynthesis [1]
Describe and explain the concept of ‘compensation point’. [4]
- Rate of photosynthesis can vary according to light intensity which increases during the day and decreases at night. Rate of respiration stays constant throughout the day [1]
- Compensation point is when the rate of photosynthesis becomes equal to the rate of respiration [1]
- which means that the amount of oxygen given out / carbon dioxide taken in during photosynthesis is equal to the amount of oxygen taking in / carbon dioxide given out during respiration [1],
- thus there is no net output of oxygen / net intake of carbon dioxide via the stomata through the process of diffusion. [1]
Cambium function
- Separates vascular tissues
- Can divide n differentiate to form new xylem n phloem tissues -> thickens stem
Xylem
- Long hollow tube stretching from root to leaf
Function:
- Transports water and dissolved mineral salts from the roots to the stem and leaves
- Provides mechanical support for the plant to prevent the plant from collapsing
Structure:
- Consists of many non-living lignified cells joined together at the ends to form a long hollow narrow tube ->reduces resistance to water flowing thru xylem
- (Lignin deposits in the inner walls of xylem vessels) + (Has diff patterns of lignification: annular, spiral, pitted)
- Narrow, hollow, continuous lumen with no cross walls, lacking in protoplasm to allow for faster transportation of water and dissolved mineral salts
Adaptations:
Long narrow hollow lumen, WITHOUT protoplasm and cross-walls → reduces resistance to water and dissolved mineral salts flowing through the xylem vessel → enabling faster rate of transport of water and dissolved mineral salts up the lumen of xylem vessel
INNER walls are lignified to provide the plant with mechanical support, and prevent the plant from collapsing.
Phloem
Function:
Transports sucrose and amino acids from the leaves to other parts of the plant
Structure:
- Contain sieve tube elements that has little protoplasm and a continuous column to allow for faster transportation of sucrose and amino acids [1]
- contains companion cell with a lot of mitochondria to release energy to load sucrose into the sieve tube elements. [1]
Sieve tube elements:
- Sieve tube cells/elements (STC) r elongated cells that lack nuclei n hv thin layers of cytoplasm
- Made up of many sieve tube cells joined end to end to form column with sieve plates in betw
- Sieve plates r cross-walls within sieve tube elements with many small sieve pores
Companion cells: (CC)
- Narrow, thin-walled cell with cytoplasm, nucleus and contains numerous mitochondria for aerobic respiration and AT
- Function: To allow active transport of sucrose and amino acids from the neighbouring mesophyll cells into sieve tube elements
Adaptations:
- Phloem sieve tube elements have very little protoplasm and are arranged to form a continuous column -> reduces resistance for faster rate of transport of sucrose and amino acids within the phloem.
- Presence of pores within the sieve plates -> allow faster rate of transport of sucrose and amino acids within the phloem.
- Companion cells have numerous mitochondria -> release more energy for active transport of sucrose and amino acids from the mesophyll cells into the phloem sieve tube cells.
- Every phloem sieve tube cell has an associated companion cell -> ensure survival of sieve tube cell.
If a sample of the phloem fluid is tested for Benedict’s Test, what do you think you will observe?
Benedict’s solution will remain blue because sucrose is not a reducing sugar.
Compare and contrast between the functions of xylem and phloem. [5]
Similarities:
- Xylem and phloem both transport substances/materials to different parts of the plant. [1]
- Xylem and phloem both transport substances as a dissolved solution to different parts of the plant. [1]
Differences:
- Xylem transports water and mineral salts from the roots to the leaves while phloem transports sucrose and amino acids from the leaves to other parts of the plant. [1]
- Xylem transports water and mineral salts in one direction up the plant while phloem transports sucrose and amino acids in both directions. [1]
- Xylem transports water and mineral salts by root pressure, transpiration pull and capillary action while phloem transports sucrose and amino acids by pressure flow as a result of loading sucrose into the phloem via active transport. [1]
Describe the adaptations of the phloem vessel in translocation of nutrients. [4]
- Sieve tube cell / element: Little protoplasm to minimise obstruction to flow [1] + Sieve tube plate with pores to facilitate efficient transport of sucrose and amino acid along the sieve tube element [1]
- Companion cells: Abundant mitochondria – release energy during respiration for active transport [1] of sucrose and amino acid into phloem and support sieve tube cell survival [1]
Organisation of vascular tissues in stems n roots similarity + differences
similarity:
- Presence of vascular bundle (found along spongy mesophyll)
Differences:
Stem:
- xylem and phloem are grouped together in the stem to form vascular bundles, arranged in a ring around pith(storage tissue)
- presence of cuticle
- absence of piliferous layer
- Xylem @ upper layer, phloem @ lower layer
Roots:
- xylem and phloem are not grouped together, they alternate
- Absence of cuticle
- Presence of piliferous layer for absorption of water through osmosis
- Epidermis, outermost layer of cells bears long & narrow extension of root hair -> ^SA:V of RHC for absorption of water&mineral salts
Root hair cell’s absorption methods
Diffusion, AT + osmosis
Diffusion/AT
When concentration of ions in the soil solution is higher/lower than that in the cell sap, Ions diffuse down/absorbed against the concentration gradient/(with th use of energy provided by cellular respiration in RHC).
Osmosis:
1. Each root hair grows between the soil particles.
2. A thin film of dilute solution of mineral salts surrounds each soil particle.
3. Water moves into the RHC and from cell to cell until it reaches the xylem vessels, down a CG, by osmosis. (Transpiration pull + lapillery action + root pressure)
Adaptations for absorption in RHCs (PMCMWP)
- Has long and narrow protrusion
- Increases surface area to volume ratio to increase rate of absorption of water and dissolved mineral salts from soil to root hair cells. - Has numerous mitochondria
- Releases more energy from higher rate of respiration for active transport of dissolved mineral salts from soil solution to the root hair cell. - Has cell membrane
Prevents the concentrated cell sap w lower wp as compared to the soil, from leaking out - Has conc cell sap with lower WP than soil solution
- Allow net movement of water molecules into the root hair cell via osmosis, down a water potential gradient.
Photosynthesis definition + condition
Process in which light energy is absorbed by chlorophyll and converted into chemical energy for the formation of glucose synthesised from CO2 & H2O. O2 is released as by-product.
6CO2 + 6H2O —(light energy, chlorophyll)-> C6H12O6 + 6O2
Conditions
- CO2
- Chloroplasts containing chlorophyll which absorbs light energy during day
- Water n dissolved mineral salts from roots
- Temperature (suitable)
- Light energy
Destarching
- A potted plant with variegated leaves is placed in the dark -> destarching (must be carried out b4 experiments)
- In darkness, photosynthesis stops n enzymes in leaves convert starch to sucrose n transported to other parts of plant
- Ensures starch is absent in leaves prior exprmt such that all starch present in leaves aft exprmts must’ve been formed during exprmt
Factors affecting rate of photosynthesis
- Light intensity
- ^ LI, ^photosynthesis until a constant rate is reached. Beyond point X, the rate of photosynthesis remains the same even though light intensity is increased. Maximum rate of enzymatic activity in chloroplast is reached (saturation) - CO2 concentration
- ^CO2 conc, ^photosynthesis, ^glucose produced, until a constant rate is rched. - Temperature
- ^tempt to optimum, ^photosynthesis. ^T beyond optimum denatures enzyme -> decreasing p~
- photosynthesis is enzyme dependent
Limiting factor
A factor that directly affects or limits a process if its quantity or concentration is altered.
Explain how rate of photosynthesis can be affected by:
Temperature [4]
- When the temperature is low, rate of photosynthesis is low as enzymes are inactive. [1]
- There is an increased in the rate of photosynthesis due to increased kinetic energy of enzymes that increase chance of successful collisions to form more enzyme substrate complex. [1]
- At optimum temperature, rate of photosynthesis is the highest as the enzymes are most active. [1]
- Beyond optimum temperature, decrease in the rate of photosynthesis enzyme is denatured due to deformed 3 dimensional shape of active site. [1]
Explain how rate of photosynthesis can be affected by:
Light intensity [3]
- Increase. More chlorophyll activated to convert more light energy to chemical energy [1]
- rate of photosynthesis increases to synthesise more glucose [1]
- Until optimum intensity is reached, light is no longer limiting [1]
Explain how rate of photosynthesis can be affected by:
Carbon dioxide concentration [3]
- Increase. Higher substrate concentration [1]; rate of photosynthesis increases to synthesize more glucose [1]
- Until maximum rate of reaction is reached, carbon dioxide concentration is no longer limiting [1]
Describe the fate of the glucose after it is synthesisd in the leaf. [4]
(Any 4)
- Excess glucose converted to starch and store in the leaf
- Convert into sucrose to load into phloem via active transport to transport to other parts of the plant via translocation
- Combine with nitrates in mineral salt to form amino acids
- Convert to fats to be stored
- Used in respiration to release energy for cellular activities
Translocation definition
The transport of manufactured food substances such as sucrose and amino acids in the phloem from leaves to all parts of plant by active transport
