Transport in plants Flashcards
Why do plants require water?
● Photosynthesis
● Maintenance of structure (turgidity)
● Cooling effect
Why do plants require mineral ions?
For growth e.g. nitrates are required to
produce proteins
Which structure in plants is adapted for the uptake of
water and minerals?
Root hairs
How is water transported into root hairs?
● Lower concentration of water in root hair cells
than in the soil
● Water diffuses down its concentration gradient
into root hair cells by osmosis
How are minerals transported into root hairs?
● Lower concentration of mineral ions in the soil
than in the root
● Root hair cells take up mineral ions by active
transport
Outline how plant roots are adapted for the
absorption of water and minerals
Plant roots are composed of millions of root hair cells which have:
● Long hairs that extend from the cell body, increasing the
surface area for absorption
● Many mitochondria which produce ATP for active transport of
mineral ions
Name the two plant transport tissues
Xylem
Phloem
What is the function of the xylem?
Transports water and dissolved mineral ions up the
plant, from the roots to the leaves via the
transpiration stream
Describe how the xylem is adapted to its function
• Hollow dead cells (no cytoplasm). • Cells walls at the end broken down (perforated end plates) so one long tube is formed. • Has lignin to make it strong to support the plant and not burst. • Is waterproof but has pits so water can only get out through these.
What is the function of the phloem?
Transports sucrose up and down the stem
from photosynthetic tissues (e.g. mature
green leaves) to non-photosynthetic tissues
(e.g. developing seeds) via translocation
What are the two cell types that make up the
phloem?
Sieve tube elements
Companion cells
Describe how the phloem is adapted to its function
- Sieve cells have little cytoplasm so it is easy for substances to pass though.
- Cell wall at each end has holes in to allow sucrose to move through.
- Has companion cells attached to it. These have many mitochondria to release energy. This is used to actively transport the sucrose into the phloem.
What is transpiration?
The loss of water vapour from the parts
of a plant exposed to the air due to
evaporation and diffusion
Where does the majority of transpiration take place?
Leaves
Describe the process of transpiration
● Water evaporates from the mesophyll cell surfaces and diffuses
out of the stomata
● Water molecules (which have cohesive properties) are drawn
up the xylem vessels to replace the water that has been lost
● This causes more water molecules to be absorbed from the soil
into root hair cells
How does the transpiration stream transport mineral ions?
Mineral ions are dissolved in the water
that is carried by the transpiration stream
What are stomata?
They are pores found in the lower
epidermis of a leaf which allow gas
exchange
What are guard cells?
Specialised cells surrounding the stoma
that change shape to control the size of
the pore
How do guard cells control the size of stomata?
To open the stomata:
Water enters guard cells by osmosis. They swell and become turgid. They bend
and draw away from each other, opening the stomata.
To close the stomata:
Water leaves guard cells. They become flaccid, closing the
stomata.
What factors affect the rate of transpiration?
● Light intensity
● Temperature
● Air movement
Describe how high light intensity affects the rate of
transpiration
● High light intensity, greater number of stomata open to allow gas
exchange for photosynthesis
● Rate of photosynthesis increases so more water is taken up from the
soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
∴ rate of transpiration increases
Describe how low light intensity affects the rate of
transpiration
At a low light intensity, fewer stomata are
open so the rate of transpiration
decreases.
Describe how temperature affects the rate of
transpiration
● Temperature increases, water molecules have more KE so rate of
diffusion increases
● Photosynthesis also increases so more water is taken up from the
soil, pushing water up the xylem
● More water vapour diffuses out of the stomata
∴ rate of transpiration increases
Describe how air movement affects the rate of
transpiration
● Air movement increases, high water concentration gradient
maintained between the air spaces in the leaf and atmosphere
● Increased rate of diffusion of water molecules out of the
stomata
● Rate of transpiration increases
What apparatus is used to measure the rate of
transpiration?
Potometer
What is assumed when measuring the rate of
transpiration using a potometer?
rate of water uptake ≈ rate of transpiration
How can the rate of transpiration be calculated using
a potometer?
rate of transpiration = distance moved by bubble/ time taken
What is translocation?
The movement of sugars (sucrose,
amino acids etc.) up and down a plant,
from the source to the sink, via the
phloem, this requires ATP.
Identify the structures of the leaf labelled
in the diagram below
https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FBiology%2FGCSE%2FNotes%2FEdexcel%2F6-Plant-Structures-and-their-Functions%2FFlashcards%2FFlashcards%2520-%2520Topic%25206%2520Transport%2520in%2520plants%2520-%2520Edexcel%2520Biology%2520GCSE.pdf
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Describe how leaves are adapted for
photosynthesis
● Broad - large surface area for light absorption
● Thin - short diffusion distance for gases, allows light to reach all cells
● Vascular bundles (xylem and phloem) form a network to deliver
water and remove glucose.Also provide support.
● Photosynthetic pigments (e.g. chlorophyll) absorb light
Describe how tissues of the leaves are adapted for photosynthesis and gas exchange
● Palisade mesophyll layer - receives most light so contains greatest
concentration of chloroplasts
● Upper epidermis - transparent, allows light to reach palisade layer
● Spongy mesophyll layer - air spaces increase the rate of diffusion
● Lower epidermis - contains many stomata for gas exchange
Describe how plants are adapted to live in hot, dry conditions
● Small leaves/spines - reduce surface area for water loss
● Thick waxy cuticle - reduces evaporation, conserving water
● Thick stem - provides a storage of water
● Shallow but widespread roots - large surface area to absorb water
● Stomata sunken in pits and leaves curled - reduces airflow, lowering
diffusion gradient and reducing water loss by evaporation
● Stomata close to reduce water loss
_____________ are used to produce proteins.
Nitrates
Describe how plants are adapted to live in cold conditions
- Deciduous trees with broad leaves lose their leaves in the winter. This prevents water loss when soil might be frozen.
- Most conifers though (e.g. pine trees) don’t do this. Instead they have needle shaped leaves with a much smaller surface area and very thick cuticles.
- Plants can also reduce water loss by trapping water vapour close to their leaves. This slows down the rate of diffusion out of the stomata. Broad leave plants often have their stomata in sunken pits. This allows them to fill with water to slow diffusion further.
