Plant Tissues, Organs & Systems (AQA GCSE Combined Science: Trilogy: Biology): Flashcards
Exam code: 8464
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Name the main plant tissues.
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Name the main plant tissues.
Epidermal tissue, palisade mesophyll, spongy mesophyll, xylem, phloem and meristem tissue.
Meristem tissue
Plant tissue found at the growing tips of shoots and roots, where cells divide to produce new cells for growth.
How is the palisade mesophyll adapted for photosynthesis?
It is made of column-shaped cells at the top of the leaf, tightly packed with chloroplasts to absorb the maximum amount of light.
What is the function of the spongy mesophyll?
It contains air spaces that increase the surface area for the diffusion of gases (e.g. carbon dioxide) through the leaf.
What are the functions of the upper epidermis and the waxy cuticle?
Upper epidermis: thin and transparent to let light pass through to the palisade layer.
Waxy cuticle: protects the leaf and reduces water loss by evaporation.
What is the role of the guard cells and stomata?
They control gas exchange and water loss.
Guard cells open and close the stomata, letting carbon dioxide in and oxygen out, and allowing water vapour to escape.
The leaf is a plant that is adapted for photosynthesis.
The leaf is a plant organ that is adapted for photosynthesis.
Which three organs make up the plant organ system for transport?
The roots, stem and leaves.
What does xylem transport, and in which direction?
Water and mineral ions, from the roots up to the stem and leaves (in one direction only).
What does phloem transport?
Dissolved sugars (mainly sucrose) and amino acids, from the leaves to the rest of the plant for use or storage.
How are root hair cells adapted for absorbing water and minerals?
They are long, thin extensions that give a large surface area.
Water is absorbed by osmosis and mineral ions by active transport.
How is xylem tissue adapted for its function?
It is made of hollow tubes of dead cells strengthened by lignin, adapted to transport water in the transpiration stream.
Root hair cells absorb water from the soil by the process of .
Root hair cells absorb water from the soil by the process of osmosis.
Transpiration
The loss of water vapour from the leaves, by evaporation at the mesophyll cell surfaces followed by diffusion of water vapour out through the stomata.
Transpiration is the loss of water from the leaves of a plant.
Transpiration is the loss of water vapour from the leaves of a plant.
Name the four environmental factors that affect the rate of transpiration.
Temperature, humidity, air movement (wind) and light intensity.
How do increasing temperature and increasing air movement affect the rate of transpiration?
Both increase the rate.
A higher temperature gives water molecules more energy to evaporate; air movement carries water vapour away, maintaining a steep diffusion gradient.
How does increasing humidity affect the rate of transpiration?
It decreases the rate.
More water vapour in the surrounding air reduces the concentration gradient between the leaf and the air, so less water diffuses out.
How do guard cells open and close the stomata?
When water is plentiful, guard cells become turgid and the stoma opens.
When water is scarce, guard cells become flaccid and the stoma closes, reducing water loss.
Why are stomata found mainly on the underside of the leaf?
The underside is cooler and shaded (lower light intensity), so this position reduces water loss by transpiration.
How is the rate of transpiration measured using a potometer?
An air bubble is introduced into the capillary tube; the plant's uptake of water pulls it along.
The further the bubble moves in a set time, the faster transpiration is occurring.
How could you change each environmental factor when investigating transpiration with a potometer?
Air movement: use a fan.
Humidity: enclose the shoot in a plastic bag.
Light intensity: move a lamp closer or further away.
Temperature: change the temperature of the room.
Translocation
The transport of dissolved sugars (mainly sucrose) and amino acids through the phloem, from source (where they are made) to sink (where they are used or stored).
What does phloem tissue transport, and from where to where?
Dissolved sugars (mainly sucrose) and amino acids, from the leaves to the rest of the plant for immediate use or storage.
How is phloem tissue structured?
It is made of living, elongated cells joined end to end.
The end walls have pores (sieve plates) that let cell sap flow from one cell to the next.
What is meant by "source" and "sink" in translocation?
Source: where sugars are made or released (e.g. the leaves in summer).
Sink: where sugars are used or stored (e.g. roots and growing tips).
The transport of dissolved food from source to sink through the phloem is called .
The transport of dissolved food from source to sink through the phloem is called translocation.
Give two differences between transport in the xylem and in the phloem.
Xylem: carries water and minerals; moves in one direction (roots → leaves); made of dead cells.
Phloem: carries dissolved sugars; moves in multiple directions (source → sink); made of living cells.
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