SB6 Flashcards
Plant structures and their functions
State the word equation for photosynthesis
Water + carbon dioxide -> Oxygen + glucose
Why is photosynthesis endothermic
- It takes in light energy
- Products have more energy than reactants
What type of plants go through photosynthesis
- Green plants
- Algae
What is the purpose of photosynthesis
- Plants make their own food (autotrophs)
- Glucose is used to make larger, complex structures
What is a plants biomass
- Its mass - which is made up of the larger, complex molecules made from glucose
Why is glucose converted into different substances
It can’t be transported by phloem
List the uses of glucose
- Respiration
- Converted into starch
- Broken down into simpler substances e.g. sucrose (can be transported by phloem)
List the uses of sucrose
- Starch conversion (storage)
- Converted into cellulose and lipids
- Glucose (respiration)
Name the factors that affect photosynthesis
- Carbon dioxide concentration
- Light intensity
- Temperature
- Amount of chlorophyll
If light and CO2 are in plentiful supply what is the limiting factor
Temperature
If temperature is right and CO2 is in plentiful supply what is the limiting factor
Light
If temperature is right and light is in plentiful supply what is the limiting factor
Carbon dioxide
Describe how to investigate the effect of light intensity on photosynthesis (Practical P)
1) Use spoon to scoop 15 algal balls into each of the 5 glass bottles
2) Use pipette to measure 6ml of the hydrogencarbonate indicator and put that into each bottle
3) Cover one of the containers with foil (control variable)
4) Set up lamp and place a meter stick in front of it
5) Place large beaker filled with water in front of the lamp
6) Place the control and a normal bottle at 20 cm mark either side of the meter stick
7) Place the rest 20 cm apart
8) Wait at least an hour then observe change in the indicators colour
Why is it important to place a beaker full of water in front of the lamp in practical P
- Absorbs lamp heat
- Heat from the lamps light doesn’t affect rate of photosynthesis
Describe the colour changes in the hydrogencarbonate indicator
- Yellow colour = more acidic = more CO2 present
- Purple colour = more alkaline = less CO2 present
Why should sodium hydrogencarbonate be added when using pondweed to investigate the effects of light intensity
- To ensure that plant has enough carbon dioxide
- So carbon dioxide is not a limiting factor
How can temperature be controlled when using pondweed
Place beaker into a water bath
Describe the graph for the effects of light intensity
- Rate of photosynthesis increases as light intensity increases
- At a certain point rate doesn’t increase (graph plateaus)
- Light intensity is no longer the limiting factor
How can you measure light intensity
Using a lux meter
What is the relationship between light intensity and distance from the lamp
Inversely proportional
What is inverse square law
Light intensity decreases in proportion to the square of the distance
What is the inverse square law equation
1/d*d
What happens if light intensity is too high
- Cells become damaged
- Cells can no longer trap sunlight
Describe the graph for the effects of carbon dioxide concentration
- As carbon dioxide concentration increases, rate of photosynthesis increases
- At a certain point, rate stops increasing (graph plateaus)
- Carbon dioxide is no longer the limiting factor
Describe the graph for the effects of temperature
- Enzyme activity is slow - not enough energy
- As temperature increases, rate of photosynthesis increases
- Temperature reaches optimum - enzyme activity is at its highest
- Temperature continues increasing, enzyme activity slows
- Enzyme activity stops as they have denatured
Why do we water plants
- Water carries dissolved ions
- Makes plant cells turgid
- Cools leaves (evaporation)
- Necessary for photosynthesis
Describe the different ways water is transported in plants
- Osmosis - into the centre of root hair cells
- Diffusion - through the cell membrane
- Transpiration stream - up the stem via the xylem
- Evaporation - out of the leaves
What is the purpose of roots
- They anchor plants to the ground
- They absorb water and dissolved mineral ions from soil
What are the adaptions of root hair cells
- Large surface area = absorb more water and ions
- Thin cell wall = shorter diffusion pathway
Define active transport
The movement of particles across a membrane against a concentration gradient using energy from respiration
Define osmosis
The movement of water molecules across a semi permeable membrane from an area of higher concentration to lower concentration
Define diffusion
The movement of particles from an area of higher concentration to lower concentration
How do mineral ions enter root hair cells
- Via active transport
- More ions inside cell than outside
Name the factors that affect transpiration
- Temperature (water evaporates and diffuses faster)
- Humidity (low humidity = water diffuse out)
- Light intensity (stomata opens wider and for longer, increasing water loss)
- Air movement (moves water away from stomata)
How are xylem cells adapted to their function
- Made of dead cells
- Walls strengthened by lignin - stay upright
- Lose the top + bottom of their cell walls forming a hollow tube
- No cytoplasm
How does transpiration work
- Caused by the evaporation and diffusion of water from plant surface
- Loss of water = shortage of water
- More water drawn up from roots through xylem to replace it
- Stream carries dissolved mineral ions
What things do you need to consider to make sure practical T doesn’t produce inaccurate results
- Ensure pipette is airtight - use vaseline between pipette and rubber tubing
- Cut stem diagonally - avoid air entering xylem
Describe how to estimate transpiration rate (Practical T)
1) Mark water level on glass pipette
2) Leave for 24 hours
3) Measure distance of new water levels
4) Repeat experiment with other variables e.g. fan, lamp and compare it with control
Why is using a potometer an indirect measurement
- Measures uptake not evaporation
How would u change humidity in practical T
Use a plastic bag
What is the stomata
Tiny pores on the surface of a plant
What is the stomata needed for
- Gas exchange
- They allow carbon dioxide and oxygen to diffuse in and out
- They allow water vapour to escape
What are the guard cells
The cells that open and close the stomata
How do guard cells control the size of the stomata
- Change shape
- Turgid - stomata open
- Flaccid - stomata closed
How are leaves adapted for photosynthesis
- Broad (large surface area) to trap more sunlight
- Waxy cuticle which reduces water loss
- Upper epidermis is transparent
- Palisade layer (has lots of chloroplasts) is an upper layer so it is more exposed to light
- Xylem and phloem help support the structure and provide water and glucose
- Spongy mesophyll layer (lots of air spaces) increase rate of gas exchange
- Lower epidermis (lots of stomata) carbon dioxide can diffuse directly into leaf
What is translocation
The transport of dissolved sugars around a plant via the phloem
How is the phloem adapted to its function
- Made of sieve tubes which do not have a nucleus and less organelles - more space for sugars and amino acids to flow
- Made of thick, rigid walls to withstand high pressures
- Has a perforated end so cytoplasm connects to next cell creating a constant flow
- Companion cells contain a lot of mitochondria to release a lot of energy required for transport
Name the main difference between the phloem and the xylem
- Phloem = bi directional
- Xylem = only upwards
Name adaptations necessary for living in extreme conditions
- Small leaves/ spines - reduce water loss (smaller SA), stop predation
- Curled leaves - reduces air flow and trap water vapour (reduce water loss)
- Thick waxy cuticles reduce water loss
- Fleshy stem which stores water
- Fewer stomata (only open at night) reduce water loss
- Stomata in sunken pits - reduce air flow close to stomata
Define tropism
Growth movement towards a stimulus
What types of tropisms are there
- Gravitropism
- Phototropism
- Hydrotropism
- Chemotropism
- Thigmotropism
What are auxins
Hormones produced by meristem cells in shoot tips
List the effects of auxins in the shoots
- Positive phototropism - auxins gather at the top and shoot grows upwards
- Positive phototropism - auxins gather on the shadier side and cells elongate faster and bend to the light
- Negative gravitropism - shoot grows sideways so there are more auxins on the lower side, this side bends upwards
List the effects of auxins in the roots
- Positive gravitropism - extra auxins on bottom inhibit growth, top half grows faster and bends downwards
- Negative phototropism - root exposed to light, more auxins on shadier side, top half grows faster and downward
Explain the effects of auxins in the roots and shoots
- Shoots - promote growth
- Roots - inhibit growth
Name the commercial uses of plant hormones
- Weedkillers
- Growing cuttings
- Controlling fruit and flower formation
- Producing seedless fruits
- Controlling the ripening of fruits
- Controlling seed germination
What is auxins commercial uses
- Weed killing - disrupt normal growth patterns and kills them
- Growing cuttings with rooting powder - cuttings produce roots and growers can create clones of plant quickly
What is gibberelins commercial uses
- Controlling flower and fruit formation - stimulate seed germination so plants can flower earlier, or reduce flowering where necessary
- Producing seedless fruit - applied to unpollinated flowers so fruit grows but seeds don’t
- Seed germination - allows seeds to germinate at any time of year or all seeds germinate at the same time
What is ethene’s commercial use
- Controlling the ripening of fruit - added during transportation so fruit will be ripe when it arrives at supermarket
