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A Level Biology OCR A > 3.1.3 > Flashcards

3.1.3 Flashcards

(67 cards)

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1
Q

What are dicotyledonous plants?

A

Plants with two seed leaves and a branching pattern of veins

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2
Q

What is the role of the meristem in plants?

A

A layer of dividing cells, specifically the pericycle

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3
Q

What does phloem transport?

A

Dissolved assimilates

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4
Q

What are vascular tissues?

A

Cells specialised for transporting fluids by mass flow

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5
Q

What does xylem transport?

A

Water and minerals

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6
Q

Why do larger plants need a transport system?

A

Smaller surface area to volume ratio, requiring specialised exchange surfaces and a transport system

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7
Q

How do plants absorb water and minerals?

A

At the roots

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8
Q

How do plants manufacture sugars?

A

By photosynthesis in the leaves

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9
Q

What is the arrangement of xylem and phloem in dicotyledonous plants?

A

Found together in vascular bundles

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10
Q

What is the central core of xylem in a young root typically shaped like?

A

An X

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11
Q

What surrounds the vascular bundle in a young root?

A

The endodermis

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12
Q

What is the function of the cambium layer in stems?

A

Divides to produce new xylem and phloem

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13
Q

Where are vascular bundles located in the stem?

A

Near the outer edge of the stem

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14
Q

What type of plants have vascular bundles that form a continuous ring in older stems?

A

Woody plants

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15
Q

What are companion cells?

A

Cells that help to load sucrose into the sieve tubes

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16
Q

What are sieve tube elements?

A

Cells that make up the tubes in phloem tissue that carry sap

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17
Q

What is the structure of xylem tissue?

A

Consists of vessels, fibres, and living parenchyma cells

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18
Q

How does lignin affect xylem vessels?

A

Makes the walls waterproof and strengthens the vessel walls

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19
Q

What prevents the xylem vessels from collapsing?

A

Lignin thickening

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20
Q

What are bordered pits in xylem?

A

Gaps that allow water to move sideways between vessels

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21
Q

What does phloem transport?

A

Sucrose and amino acids

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22
Q

What is the main function of sieve plates?

A

Allow movement of sap from one sieve tube element to another

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23
Q

What is the role of companion cells in phloem?

A

Carry out metabolic processes needed to load assimilates into sieve tubes

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24
Q

What are plasmodesmata?

A

Gaps in the cell wall containing cytoplasm that connects two cells

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25
What is the apoplast pathway?
Water passes through spaces in the cell walls and between cells
26
What is the symplast pathway?
Water enters the cell cytoplasm through the plasma membrane
27
What is the vacuolar pathway?
Similar to the symplast pathway, but water can enter and pass through vacuoles
28
What is water potential?
A measure of the tendency of water molecules to move from one place to another
29
What happens to a plant cell placed in a salt solution with a very negative water potential?
It will lose water by osmosis
30
What is plasmolysis?
Condition where the plasma membrane loses contact with the cell wall
31
What is transpiration?
The loss of water vapour from the aerial parts of a plant
32
Where does most water vapour leave the plant?
Through the stomata
33
What is the transpiration stream?
Movement of water up the stem to replace lost water
34
What effect does light intensity have on transpiration rate?
Higher light intensity increases the transpiration rate
35
How does temperature affect transpiration?
Higher temperature increases evaporation, diffusion, and decreases relative humidity
36
What effect does relative humidity have on transpiration?
Higher relative humidity decreases the rate of water loss
37
How does air movement affect transpiration?
Carries away water vapour, maintaining a high water vapour potential gradient
38
What is a potometer?
A device that measures the rate of water uptake as a leafy stem transpires
39
What precautions should be taken when using a potometer?
1. Set up under water 2. Ensure shoot is healthy 3. Cut stem under water 4. Cut stem at an angle 5. Dry the leaves
40
What is the formula for calculating the volume of a cylinder?
v = πr^2l
41
What is the first step in preparing a shoot for measurement?
Ensure that the shoot is healthy
42
What is the rate of transpiration?
Rate = volume/time
43
Define adhesion in the context of water movement in plants.
The attraction between water molecules and the walls of the xylem vessel
44
Define cohesion in the context of water movement in plants.
The attraction between water molecules caused by hydrogen bonds
45
What drives the transpiration stream?
The water potential gradient between the soil and the air in the leaf air spaces
46
What are root hair cells?
Cells with a long extension that increases the surface area of the root, absorbing mineral ions and water
47
What is the role of the endodermis in water movement?
It drives water movement through an active process and contains the Casparian strip
48
What does the Casparian strip do?
Blocks the apoplast pathway between the cortex and the medulla
49
What is root pressure?
Pressure in the root medulla that pushes water into the xylem
50
Describe transpirational pull.
The pull of water molecules up the xylem due to evaporation from leaves
51
What is the cohesion-tension theory?
It explains water movement in plants due to cohesion and tension in the water column
52
How does capillary action help water movement in plants?
Adhesion attracts water molecules to the sides of the xylem
53
Where does most water leave the plant?
Via the stomata
54
What is a hydrophyte?
A plant adapted to living in water or very wet conditions
55
What is a xerophyte?
A plant adapted to living in dry conditions
56
List adaptations of terrestrial plants to reduce water loss.
* Waxy cuticle on leaves * Stomata on the under-surface of leaves * Stomata closed at night * Deciduous plants lose leaves in winter
57
What adaptations does marram grass have for arid conditions?
* Rolled leaves to trap humid air * Thick waxy cuticle * Stomata on the inner side of rolled leaves * Stomata in pits covered by hairs * Dense spongy mesophyll with few air spaces
58
What are the adaptations of cacti to survive in arid conditions?
* Succulent stems that store water * Reduced leaves to spines * Green stems for photosynthesis * Widespread roots
59
What is a hydathode?
Specialized structures that release water droplets from the leaf surface
60
What is translocation in plants?
The movement of assimilates throughout the plant via the phloem
61
What is a source in plant transport?
A part of the plant that loads materials into the transport system
62
What is a sink in plant transport?
A part of the plant where assimilates are removed from the transport system
63
What is active loading in phloem transport?
The process of loading sucrose into the sieve tube using energy from ATP
64
Describe how sucrose moves along the phloem.
By mass flow, caused by a difference in hydrostatic pressure
65
How does water enter the sieve-tube element at the source?
By osmosis from surrounding tissues due to lower water potential
66
What happens to water potential when sucrose is removed from the phloem?
It becomes less negative, allowing water to move out
67
True or False: The sap in the phloem can flow in either direction.
True

A Level Biology OCR A (2 decks)

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