UNIT 6 Plant Nutrition - Photosynthesis Flashcards
A student set up the apparatus shown in Fig. 3.1 to investigate the effect of light intensity on
the rate of photosynthesis of a pond plant.
The student maintained the temperature at 20 o
C and measured the distance travelled by the air bubble in the capillary tube for a period of five minutes on three occasions for each light intensity.
The student’s results are shown in Table 3.1 on page 8.
(a) (i) Explain why the student included the glass tank and the syringe in the apparatus.
glass tank?
syringe?
glass tank - absorbs heat from lamp
syringe - reposition the air bubble / return air bubble to top of tubing
State three functions of water in plants.
maintaining cell turgidity ;
preventing wilting ;
transport of minerals / amino acids / sugars ;
medium for enzyme action ;
raw material for photosynthesis;
(ii) Explain why the air bubble moves down the capillary tube.
THREE OF:
⭐ 1 photosynthesis produces oxygen/plant releases oxygen
⭐ 2 oxygen is, by-product (of photosynthesis) ;
3 from splitting of water / photolysis ;
4 oxygen comes out of solution / AW ;
⭐ 5 gas, collects / rises to the top ;
6 (gas) pushes water down the tube / displaces the water ;
Interpolation - notice pattern. each mm distance = 0.2 mm/min rate of photosynthesis so 7mm distance, 0.2 x 7 = 1.4.
In graph, what should you make sure of?
all points plotted accurately ;
curved or straight line of best fit / straight lines between points ;
ignore if line continues beyond first and last points because of (c)(i)
R if line goes to 0
[allow a straight line of best fit that is close to the plotted
points]
“Using the graph to help you,” should you extrapolate?
NO - just use graph given/what you drew
(ii) Explain why the rate of photosynthesis decreases as the distance of the lamp
from the pond plant increases.
1 (increase distance gives) decrease light (intensity) ; ORA
2 ref. to light energy ;
3 absorbed by, chlorophyll / chloroplast ;
4 light (intensity) is limiting (factor) ;
So: “Increase in distance gives decrease in light intensity. Less light absorbed by chloroplast. Light intensity is the limiting factor.”
Why upper epidermis is transparent
Allows light through
Light reaches chloroplasts
In the palisade cells
Chloroplasts need light for photosynthesis
Why plants store starch
Use it as an energy store
When plant cannot photosynthesise (no sunlight)
Why plants take up CO2 during photosynthesis
Carbon dioxide is a reactant of photosynthesis
Diffuses into leaf due to lower concentration inside of the leaf
Why chlorophyll removed from leaf before testing for starch
Chlorophyll masks the colour change (shown with iodine)
Explain the importance of the control plant in an investigation for the need of CO2 in photosynthesis
To show that the factor under test (CO2’s effect on photosynthesis) is responsible for the change observed
Explain why plants were destarched
to be sure that starch is produced during the experiment
Destarched plant. Why does the concentration of CO2 increase?
No photosynthesis
Plant respires
Carbon dioxide produced
Plant GIVES OFF which gas?
[means PRODUCT]
Oxygen
Raw materials? = ?
= ??
Raw materials = REACTANTS
in photosynthesis? Carbon dioxide and water
Line for light intensity if the experiment was repeated with higher light intensity.
Phrase to rmbr?
Same trend/looking line, but higher/above it
Remember: “Rate of photosynthesis would increase then start to level off.”
Even if chloroplasts are absent, does respiration occur?
Yes, it does
3 uses of energy in organisms (not reproduction)
Growth
Movement
Active transport
Phloem - transport sucrose & amino acids in plants
Uses of carbs & amino acids in plants?
MEMORISE:
Carbs -
⭐ For cell walls (glucose to cellulose)
⭐️ Converted to sucrose to be transported through phloem vessels
⭐ Starch storage
⭐ For energy/respiration
⭐ To attract insects to flowers
Amino acids -
⭐ To make hormones and enzymes
⭐ For growth & repair
Predict & explain what happens to rate of photosynthesis if temperature exceeds 45 degrees Celsius.
Rate of photosynthesis decreases
Bc enzyme’s active sites are denatured
For photosynthesis,
STATE:
⭐ Definition of photosynthesis
⭐ Word equation of pho. + “in the presence of…”
⭐ Definition of chlorophyll
⭐ What chlorophyll does
⭐ Chemical equation of pho.
⭐ Photosynthesis: the process by which plants synthesise carbohydrates ⁽ᵍˡᵘᶜᵒˢᵉ⁾ from raw
materials ⁽ᴴ²ᴼ & ᶜᴼ²⁾ using energy from light ⁽ᶜᵃᵗᵃˡʸˢᵗ⁾
⭐ Word equation for photosynthesis as:
carbon dioxide + water → glucose + oxygen
in the presence of light and chlorophyll
⭐ Chlorophyll is a green pigment that is
found in chloroplasts
⭐ Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
⭐ Balanced chemical equation for photosynthesis as:
6CO2 + 6H2O → C6H12O6 + 6O2
⭐ Subsequent use and storage of the carbohydrates made in photosynthesis, limited
to:
(a) starch as an energy store [in plants]
(b) cellulose to build cell walls [from glucose]
(c) glucose used in respiration to provide energy
(d) sucrose for transport in the phloem (vessels) - [glucose converted to sucrose]
(e) nectar to attract insects for pollination
Leaf adaptations -
Gases enter through special holes called stomata. These holes are opened & closed by guard cells. Once gases are in the leaf, they can diffuse easily bc there are air spaces in the spongey mesophyll layer. The cell membranes of the leaf cells allow gases & water to pass freely in & out of the cell.
Some leaf cells contain a pigment called chlorophyll which absorbs light energy. This pigment for photosynthesis are found in special organelles called chloroplasts. Most of these are found in the palisade layer at the top of the leaf. The cuticle and epidermal cells are transparent so that light can pass easily through to the chloroplasts.
Most leaves have a ⭐ large surface area to maximise exposure to sunlight for absorption of light & allows more diffusion of CO2
and are ⭐ thin, aiding in diffusion of oxygen and carbon dioxide, speeding up the exchange of the gases
+
“Thin - allows faster diffusion of CO2 to palisade mesophyll cells.”
MEMORISE -
Leaf structures in a dicot plant
Refer to printed diagrams + class worksheet.
PARTS - Upper epidermis, chloroplasts, palisade mesophyll tissue, spongey mesophyll tissue, air space, vascular bundle (xylem & phloem), lower epidermis, guard cells, stoma
Guard cells & stomata
Guard cells allow gas exchange and control water loss within the leaf
In the lower epidermis, guard cells open & close the stomata to allow carbon dioxide into the leaf and oxygen to diffuse out as well as water vapor
Stomata: allows oxygen out of cells & allows carbon dioxide in
[Site where water is evaporated from the leaf]
(Waxy) cuticle
Allows light to pass through whilst protecting the leaf’s surface
Waxy but thin, so protects leaf from water loss without blocking sunlight
Epidermal cells
Upper epidermis
Offers protection but thin to allow light through
Thin & transparent, so allows more light to reach the palisade cells
Palisade cells
/ palisade mesophyll
⭐ Contains many chloroplasts, able to absorb more light from top layer
⭐ Packed tightly together
⭐ Maximises surface area
⭐ Large vacuole pushes chloroplasts to edges of cell
⭐ Thin cell walls to aid gaseous exchange
Chloroplasts
Contains chlorophyll that absorbs light for photosynthesis
Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates
Spongey mesophyll
⭐ Irregular shaped
⭐ Fewer chloroplasts
⭐ Smaller than palisade cells
⭐ Spaced out with air pockets in between, allowing CO2 to easily diffuse through the leaf
Air space
increase surface area for gas exchange and allow gases to move more easily.
Vascular bundle - xylem & phloem
XYLEM vessels - transports water and mineral ions taken up from the soil by the roots to the stem and leaves
+ support
PHLOEM - transport sucrose & amino acids in plants AWAY from leaf to the rest of the plant
transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
Explain the importance of:
(a) nitrate ions for making amino acids
(b) magnesium ions for making chlorophyll
a) ⭐ Nitrates needed for proteins - old leaves start to dry out bc not enough nitrogen to maintain proteins in all cells
⭐ Nitrate deficient plants -
➡ stunted growth
➡ leaves (usually near growing tip) start to turn yellow
b) 🌌 Magnesium required for chlorophyll
🌌 Lack of chlorophyll production will make yellowing occur between the veins of leaves (chlorosis), starting from the lower leaves
🌌 Slow down growth of plant
Identify and explain the limiting factors of photosynthesis in different environmental
conditions
What is a limiting factor?
What’s it mean?
Main limiting factors of photosynthesis?
Limiting factor: something that is in short supply that restricts a process
+ “present in an environment” “life processes”
When a process depends on 2 or more factors (variables), the rate of that process is determined by the factor which is in shortest supply.
➡ ⭐ light intensity, ➡ ⭐ carbon dioxide concentration, ➡ ⭐ temperature
Light intensity
- Rate of photosynthesis increases with light intensity
- When intensity of light increases to a certain point, photosynthesis cannot go any faster.
[Actual maximum varies.]
Meaning of horizontal line on one of these graphs? Abt limiting factors
Means the limiting factor has changed
Carbon dioxide concentration
- Increasing CO2 concentration increases rate of photosynthesis
- There’s a maximum rate where adding more CO2 will have no more effect/photosynthesis cannot go any faster
Temperature
- Too much heat damages enzymes & causes them to denature
- Too much heat also evaporates water out of leaves & forces stomata to close
- Too little heat can reduce enzyme’s reaction rate by reducing number of collisions between the enzyme’s active site and substrate
Ratio of photosynthesis to respiration
The ratio of photosynthesis to respiration in plants changes over the day cycle
Plants are constantly respiring & releasing carbon dioxide
Plants only photosynthesise during the day when sunlight is available, taking in carbon dioxide
Investigations - Gas Exchange
Hydrogen carbonate indicator -
Hydrogen carbonate indicator is a pH indicator that changes colour depending on the pH of a solution.
CO2 is acidic. Higher CO2 concentration = more acidic
//
Investigate the effect of light on the net gas exchange in an aquatic plant using a hydrogen carbonate indicator.
Highest |CO₂| = yellow.
Higher |CO₂| = orange.
⬆ More respiration than photosynthesis. Lower pH, more acidic.
Atmospheric level = red.
⬆ Photosynthesis = respiration.
Lower |CO₂| = magenta.
Lowest |CO₂| = purple.
⬆ More photosynthesis than respiration. Higher pH, more alkaline.
INVESTIGATIONS - Gas Exchange
⭐ Several leaves from the same plant are placed in closed/stoppered boiling tubes containing some hydrogen carbonate indicator
The effect of light can then be investigated over a period of a few hours.
Tube 1-3, contents, conditions, indicator colour, reason?
Tube 1: Leaf. In the light. Purple. The overall absorption of CO2 by leaf is high in light conditions.
Tube 2: Leaf. Dark. Yellow. The overall release of CO2 from the leaf is higher in dark conditions.
Tube 3: NOOO leaf. Light. Red. This is the CONTROL - since there’s no leaf, the level of CO2 is the same as that of the atmosphere.
Net Carbon Dioxide - day vs night
During the day, plants photosynthesise faster than they respire, esp. when sun bright & light intensity high
➡ NET INTAKE of carbon dioxide in the DAY
[higher output of CO2]/if light bright enough, rate of CO2 absorption becomes greater than rate of CO2 release.
During the night, plants respire more than they photosynthesise,
➡ NET RELEASE of CO2 at NIGHT
Factors needed for photosynthesis?
⭐ Chlorophyll - helps absorb the light required
⭐ Light - provides the energy to drive the reaction
⭐ Carbon dioxide - reactant in photosynthesis to be converted to sugars like glucose
Investigate need for chlorophyll, light
& carbon dioxide [necessary factors] for photosynthesis, using appropriate controls
Investigate && describe the effects of varying
light intensity, carbon dioxide concentration and
temperature [limiting factors] on the rate of photosynthesis
- Removing starch from plant before investigation:
- Using iodine test for starch to see need for chlorophyll
- Removing chlorophyll using ethanol
- Boiling to soften
+ etc.!
Why can’t leaves be tested for glucose?
NEED FOR CHLOROPHYLL
bc it’s quickly used, converted & transported/stored as starch.
Why can the leaf be tested for starch instead?
NEED FOR CHLOROPHYLL
Starch is stored in chloroplasts. Testing a leaf for starch using iodine is a reliable indicator of which parts of the leaf are photosynthesising.
NEED FOR CHLOROPHYLL (boil, ethanol, soften by boiling, white tile w/ iodine, indicates…?):
Leaves tested for starch
If it is orange-brown, starch is not present bc photosynthesis hasn’t occurred since there’s NO chlorophyll present.
If it is blue-black, starch is present & has been stored meaning photosynthesis occurred bc chlorophyll WAS present.
To prove chlorophyll IS needed for pho, we use a VARIEGATED leaf bc partially green, partially white, so only parts of leaf contain chlorophyll
Chlorophyll ⭐
➡ A leaf dropped in boiling water to kill the cells & break down the cell membranes so iodine can seep in && so it’s permeable
[Beaker, leaf in boiling water, Bunsen burner on]
➡ Leaf left for 5-10 mins in hot ethanol in a boiling tube, removing the chlorophyll so colour change from iodine can be seen more clearly, decolourising the leaf
[Boiling tube, ethanol, Bunsen burner OFF, ethanol turns green]
➡ Leaf dipped/rinsed in boiling water to soften it
➡ Leaf is spread out on a white tile & covered with iodine solution
[Reason: iodine will change colour in presence of starch]
⭐ Green leaf ➡ entirely blue-black, photosynthesis occurring in all areas of leaf
Test whether chlorophyll is needed for pho. by using a VARIEGATED leaf (one partially green & partially white)
🔗 White areas of leaf - no chlorophyll (so orange/brown/yellow)
= orange-brown = no photosynthesis occurring = no starch is stored
🔗 Only areas containing chlorophyll stain blue-black as starch will be present.
⭐ Testing a variegated leaf for starch: Take care; ethanol is extremely flammable, turn off Bunsen burner. To heat ethanol, electrical water bath INSTEAD OF beaker w/ Bunsen burner & an open flame.
Investigating the need for LIGHT 💡🌞
SAME procedure
Destarched, aluminium foil, tested for starch w/ iodine
Light ⭐
➡ Plant needs to be destarched: before starting exper. - place plant in a dark cupboard for 48 hours
Ensures any starch already present in the leaves will be used up & won’t affect experiment’s results bc plant can’t photosynthesise, so use all starch for respiration
➡ After, a leaf of the plant can be partially covered with aluminium foil & the plant placed in sunlight for a day.
➡ A leaf dropped in boiling water to kill the cells & break down the cell membranes so iodine can seep in && so it’s permeable
➡ Leaf left for 5-10 mins in hot ethanol in a boiling tube, removing the chlorophyll so colour change from iodine can be seen more clearly, decolourising the leaf
➡ Leaf dipped/rinsed in boiling water to soften it
➡ Leaf then removed and tested for starch using iodine.
🔗 Area of leaf COVERED WITH ALUMINIUM FOIL will remain ORANGE-BROWN
bc it did not receive any sunlight & could not photosynthesise.
while…
🔗 Area EXPOSED TO SUNLIGHT will turn BLUE-BLACK.
This proves light is necessary for photosynthesise and production of starch.
Investigating the need for CARBON DIOXIDE
Destarch, place 1 in bell jar w/ NaOH (absorb CO2) & 1 w/ water (control), place in light, test for starch using iodine, one w/ NaOH remains orange-brown
Exper. uses: potted plants, clear plastic bag tied over pots, LIGHT, glass containers, THEN one has sodium hydroxide solution to absorb CO2 + soda lime at top to absorb CO2. The other w/ beaker of water.
Carbon Dioxide ⭐
➡ Destarch 2 plants by placing in a dark place for a prolonged period of time (48 hours)
➡ Place 1 (potted) plant in a bell jar which contains a beaker of sodium hydroxide, which will absorb carbon dioxide from the surrounding air. Soda lime to absorb CO2.
➡ Place the other (potted) plant in a bell jar which contains a beaker of water (control experiment), which will NOT absorb CO2 from the surrounding air.
⬆ Clear plastic bag tied over the pot.
➡ A leaf dropped in boiling water to kill the cells & break down the cell membranes so iodine can seep in && so it’s permeable
➡ Leaf left for 5-10 mins in hot ethanol in a boiling tube, removing the chlorophyll so colour change from iodine can be seen more clearly, decolourising the leaf
➡ Leaf dipped/rinsed in boiling water to soften it
➡ Place both plants in bright light for several hours.
➡ Test both plants for starch using iodine.
➡ Leaf, from plant placed near:
- Sodium hydroxide (NO PHO.), will remain orange-brown bc it could not photosynthesise due to lack of carbon dioxide.
- Water (DOES PHO.), should turn blue-black as it had all necessary requirements for photosynthesis.
INVESTIGATING THE RATE OF PHOTOSYNTHESIS
Investigate + desc. effects of varying light intensity, CO2 concentration &
temp. [limiting factors] on the rate of photosynthesis
Factors affecting rate of pho. ->
⭐ Light intensity
⭐ Carbon dioxide concentration
⭐ Temperature
To investigate how fast pho. is happening, use an aquatic plant that photosynthesises in water & count the number of oxygen bubbles it releases in a minute
As pho. occurs, oxygen gas is made & released
Since the plant is in water, the oxygen released can be seen as bubbles leaving the plant.
The number of bubbles produced over a minute can be counted to record the rate.
The more bubbles produced per minute the faster the rate of photosynthesis.
Investigating Varying Light Intensity
Equipment: lamp, ruler, water [with sodium hydrogen carbonate], thermometer [to monitor temperature], [inverted] boiling tube, O2 bubbles, [inverted] funnel, aquatic plant
To change the light intensity, the lamp may be moved to different distances away from the beaker containing the plant. The number of bubbles produced per minute should be recorded at these different distances.
Graph is one with a positive slope then horizontal line.
Rate of pho. = y-axis
Light intensity (%) = x-axis.
Mid-point of positively sloped line = increasing light intensity/CO2 concentration increases the rate of photosynthesis.
At the corner between sloped & horizontal line, SOME OTHER FACTOR becomes LIMITING.
At end of horizontal line, the rate becomes constant.
Investigating Varying CO2 Concentration
Equipment: lamp, 1% sodium hydrogen carbonate solution, thermometer [to monitor temperature], [inverted] boiling tube, O2 bubbles, [inverted] funnel, aquatic plant
To change the CO2 concentrations, different amounts of sodium hydrogen carbonate may be dissolved in the water in the beaker. The number of bubbles produced per minute should be recorded for these different CO2 concentrations. The resulting data will produce a graph like this.
Investigating Varying Temperature
Equipment: lamp, water [with sodium hydrogen carbonate], hot plate [to change temperature], thermometer [to monitor temperature], [inverted] boiling tube, O2 bubbles, [inverted] funnel, aquatic plant
The temperature of the water in the beaker may be changed to different levels & the number of bubbles produced per minute may be recorded at these different temperatures.
The resulting data will produce a graph like this:
Lopsided curve leaning to the right.
Mid-point of first part of curve = Rate increases as number of collisions between enzyme’s active sites and substrates increases.
Top point = optimum temperature.
Mid-point of second negatively sloped half of curve = Rate DECREASES as enzymes start to denature.
In which order does water pass through these structures in a plant?
A mesophyll → root hair → xylem
B mesophyll → xylem → root hair
C root hair → mesophyll → xylem
D root hair → xylem → mesophyll
D))
root hair → xylem → mesophyll
formed FIRST in a leaf as a result of photosynthesis?
glucose
which part of a leaf does most water evaporate during transpiration?
the spongy mesophyll cells
Partially permeable in plants?
Vacuole
Cell membrane
Which cell type absorbs the most carbon dioxide during the day?
Palisade mesophyll cell
Suggest and explain the reasons for the shape of the graph in region Y.
“Rate of photosynthesis levels off as the limiting factor changes.
Carbon dioxide concentration is no longer limiting factor. Light intensity could be limiting, temperature could be limiting.
Temperature affects activity of enzymes as too high can denature and too low can reduce enzyme’s reaction rate by reducing number of collisions between the enzyme’s active site and substrate”
Counting bubbles may not be the best way to measure the rate of photosynthesis. The volume of the bubbles is not always exactly the same.
Suggest and explain one alternative way of measuring the gas given off to solve this problem. [3]
measure volume (of oxygen/ gas) ;
use, inverted test-tube/ measuring cylinder/ syringe (barrel) ;
reference to, graduations /markings ; A ‘take readings from…’/ ‘record
results…’
filled with water ;
Explain why the concentration of carbon dioxide has increased between 1959 and 2013.
use/ combustion/ burning, of fossil fuels ;
reason for increased demand for energy ;
carbon dioxide from, volcanic activity / volcanoes ; deforestation ;
burning of, forests / trees ;
Global warming is largely due to this increase in atmospheric carbon dioxide.
Explain how increases in atmospheric carbon dioxide concentrations contribute to global warming.
carbon dioxide is a greenhouse gas ;
(enhanced) greenhouse effect (in context of carbon dioxide) ;
heat/infra-red/ long wavelength radiation, radiated/ emitted, from /
absorbed/ trapped/AW, by, carbon dioxide/ greenhouse gases ;
travels /AW, back to the surface ;
heat cannot, leave (from the atmosphere)/ pass into outer space ;
With reference to the water potential gradient, explain why plants may die when
grown in salty soil. [3]
salt concentration in soil is higher than in roots AW ;
ref. to water potential is greater in root cells than in soil / w.p gradient
goes from cells to soil AW;
so water is drawn out of roots + by osmosis ;
cells become flaccid ;
plant wilts ;
plant lacks water ;
An article in a school science magazine stated, ‘Many plants contain genes which
enable them to pump salts out of their roots. These genes can be made more active by
genetic engineering, enabling the plants to remove salts
before the plants are damaged.’
Explain whether you think that the process described in the article above is an example
of genetic engineering.
the removal of a gene from one species ;
and its insertion into another species ;
(in article) genes are modified, not transferred AW ;
Explain the difference in growth between the plants watered with low concentrations and those watered with high concentrations of salt solution.
salt lowers the water potential ;
plants absorb less water ;
loss of turgidity ;
less water for chemical reactions;
less, water for photosynthesis ;
stomata close ;
Plants grown in soils of pH 10 may show symptoms of deficiency. They are stunted and their leaves are yellow.
Explain how deficiencies of magnesium ions and nitrate ions lead to the symptoms
described.
magnesium ions
nitrate ions
magnesium ions
needed for making chlorophyll ;
without chlorophyll plant, not green / yellow ;
cannot absorb (much) light ;
little / no, (energy for) photosynthesis ;
nitrate ions
needed to make amino acids ;
amino acids to proteins ;
protein needed for growth ;
