Chapter 6 - Plants - Random Questions Flashcards
What is a limiting factor?
A factor which inhibits growth/ anything in short supply that prevents photosynthesis occurring at its maximum rate
What is the role of the green pigment ‘chlorophyll‘?
To transfer energy from the environment and use it to synthesise glucose from carbon dioxide and water
List ways in which glucose (produced by photosynthesis) is used in plants
- used for respiration
- used to produce cellulose to strengthen cell walls
- converted into insoluble starch for storage
- used to produce fats or oils for storage
- used to produce amino acids for protein synthesis
What are palisade cells?
Regular-shaped cells that have lots of chloroplasts. Most photosynthesis talks place in this layer
What do guard cells do?
They control the stomata - close when there is no water available
Where does water evaporate from and through what process?
From the leaves through the stomata - transpiration
Where does a plant get the reactants it needs for photosynthesis from?
Carbon dioxide - through stomata
Water - through roots
Light - from sun
How do plants conserve water?
- have wide shallow roots to collect as much water as possible
- have smaller leaf surface area so less water is lost through transpiration
- thick cuticles prevent water loss between cells
What do root hairs do?
Enlarge the surface area of the root meaning that more water (and minerals) can be absorbed into the plant by osmosis. The cellulose in the cell wall helps absorb the water
How does water get from the soil to the roots?
Osmosis
Where does water go when it is in the roots?
Travels up the plant, through the xylem, to all the cells that require water
What is lignin?
The special chemical that water-proofs xylem vessels. It stops water leaving the vessels by osmosis (impermeable) as it passes up the plant (so that not all the water gets used up straight away by cells at the bottom and therefore let some get to the top)
How are sugar and other nutrients from the leaves transported, and what is this process called?
Through the phloem - transported from leaves (where they are produced in the form of sap) to places in the plant where they are needed - translocation
List properties of a xylem vessel:
- only up
- transports water and minerals
- no end walls between cells
- thick walls stiffened with lignin
- dead tissue - empty tube
TRANSPIRATION
List some properties of a phloem vessel:
- transports water and food (sap)
- cells have end walls with perforations - sieve tube elements (porous cell walls, nutrients can flow between)
- companion cells
- two way flow
- living tissue/ cells
TRANSLOCATION
What is the transpiration rate?
The rate at which water escapes out of a plant
Name some factors that effect the transpiration rate and explain how:
~ temperature - the warmer it is, the more kinetic energy in the water particles and the faster the water evaporates
~ humidity - if high humidity, rate is low as the air is already full of water
~ wind speed - the windier it is, the faster moist air is taken away from the leaf surface (dryer air) so the concentration gradient is bigger and the transpiration rate increases
~ light intensity - transpiration is faster when the stomata are open in the light
~ surface area of leaf - large surface area, more stomata, more water loss (higher rate of transpiration)
Why do all plant tissues require water to survive?
For support and photosynthesis
What is osmosis?
The movement of water from an area of high concentration to an area of low concentration through a partially permeable membrane
What are stomata?
Holes on the underside of the leaf, through which gases move in and out
What are plasmodesmata?
Small holes that make up the sieve
What are sieve tube elements?
Porous cell walls in phloem vessels that nutrients can flow between - freely permeable membranes (anything can pass through)
What is translocation?
The movement of assimilates (sugars and other chemicals), made by plant cells , along the phloem
How does the time of year effect the movement in the phloem (translocation)?
- in summer - movement down to roots
- in spring - movement up to shoots and leaves
What is the main assimilate?
Sucrose - plants makes glucose in photosynthesis, but turns it into sucrose
Where do sugars move to and from?
They move from a source to a sink
What is the source?
Anywhere sucrose is released into the phloem (where it is made)
What is the sink?
Anywhere sucrose is removed from the phloem (where it is used)
How are companion cells adapted to their function?
They have lots of mitochondria
What is ATP?
A very unstable molecule released by mitochondria (energy)
Describe how sugar gets into the phloem
- Companion cells use ATP to actively transport hydrogen ions into the surrounding tissue
- This creates a diffusion gradient with a high concentration of hydrogen ions outside the companion cells
- Hydrogen ions move back into companion cells using co-transporter proteins
- This causes concentration of sucrose in the companion cells to increase
- Sucrose moves from companion cells to the sieve tube elements using plasmodesmata
Why are co-transporter proteins needed, and what is this called??
The molecules are too big to move by theirselves - facilitated diffusion
What can be used to measure transpiration?
Potometer
How can the rate of transpiration be observed when using a Potometer?
The rate is the speed (d/t) that the bubble moves across the tube
What is active transport and give an example?
Low concentration to high concentration
Eg. Minerals from soil into plant
What is a disadvantage to a plant closing its stomata?
Gas exchange cannot happen meaning that carbon dioxide can’t get it. This results in photosynthesis not being able to take place, meaning no oxygen or glucose is created. These are needed for respirating to take place, so the plant will suffocate
What are hormones?
Chemical messengers
Where do hormones travel?
Through the phloem (sap)
Where are hormones produced?
In the meristem (tip of plant)
What is controlled by hormones?
~ growth - roots and shoots, seed germination, leaf fall, disease resistance, fruit formation and ripening, flowering time, bud formation
~ sensitivity - responding to the environment - can make adjustments to survive
What is a tropism?
A growth response because of a stimulus
What is phototropism?
A growth response to light
What is geotropism/ gravitropism?
Growth response to ground
What is special about the hormone ‘auxin‘?
The sunlight breaks them down, so the shoot tip (which has direct sunlight) will have the least amount of auxins
Describe the relationship between the concentration of auxins and growth in the shoots
Any concentration promotes growth (auxins promote elongation of cells)
Describe the relationship between the concentration of auxins and growth in the roots
High concentration inhibits growth (auxins prevent elongation of cells), small concentration promotes growth
What are gibberellins?
Hormones that are important in starting off the seed germination (sprouting) process
What is ethene?
A hormone that is a gas and controls cell division, leaf fall and the ripening of fruits
What do auxins cause when they gather on the shaded side?
Increased cell elongation on the shaded side (grows longer)
What are 5 limiting factors of photosynthesis?
- light intensity
- water
- carbon dioxide
- temperature
- chlorophyll
What is the optimum temperature for plant growth?
21˚C
What is light intensity measured in?
Lux
What is the inverse square rule?
Light intensity = 1/distance^2
What do the graphs look like for the different factors?
Light intensity —> curved (inverse square rule)
Water, carbon dioxide + chlorophyll —> go up, then flatten when another factor becomes limiting
Temperature —> up and then down when enzymes denture
What do chlorophyll and light act as?
Catalysts
What do plants need minerals for?
To build complex molecules they need to survive and grow
What can be done to establish which mineral a plant is deficient in?
Tests or a general purpose NPK (nitrogen, phosphorus, potassium) fertiliser added
What are nitrate ions used for?
Building proteins and growth
What are phosphate ions used for?
Respiration and growth
What are potassium ions used for?
Respiration and photosynthesis
What are magnesium ions used for?
Photosynthesis
What are nitrate deficiency symptoms?
Poor growth and yellow leaves
What are phosphate deficiency symptoms?
Poor root growth and discoloured leaves
What are potassium deficiency symptoms?
Poor flower and fruit growth, discoloured leaves
What are magnesium deficiency symptoms?
Yellow leaves
Why is nitrate needed in plants?
All amino acids contain nitrogen. Amino acids are the building blocks of protein
Why is phosphate needed in plants?
A component of DNA molecules and cell membranes
Why must potassium be present in plants?
For photosynthesis and respiration enzymes to work
Why is magnesium needed in plants?
Chlorophyll molecules contain magnesium ions. It’s the magnesium that makes chlorophyll green
What are xerophytes?
Plants with adaptations to live in the dry (eg. Succulents, cactus)
- have thick leaves, grow slowly etc.
What is transpiration?
The movement of water through and out of a plant (through xylem)
