AS1 Chapter 6 - Tissues and Organs Flashcards
1
Q
What is a tissue?
A
Tissues are groups of cells of the same type that carry out the same (or a very small number of) functions.
2
Q
What is an organ?
A
An organ is a structure that consists of several different tissues, each performing different functions that contribute to the overall functioning of the organ.
3
Q
What are the major tissue layers in the ileum?
A
From innermost to outermost: Mucosa Muscularis mucosa Submucosa Muscularis externa Serosa
4
Q
What is muscle?
A
In animals muscle is contractile tissue allowing movement.
5
Q
What is mesophyll?
A
In plants mesophyll is the photosynthetic tissue in leaves.
6
Q
Animals and plants are …
A
Multicellular
7
Q
Cells become specialised according to their …
A
Function
8
Q
Give an example of an organ in plants
A
The leaf
9
Q
Give an example of a mammalian organ
A
The ileum
10
Q
Where is the ileum found?
A
The small intestine
11
Q
What is the function of the ileum?
A
- Final stages of digestion
- Absorption of the products of digestion
- Movement of undigested material along to the large intestine
12
Q
What is the overall role of the tissues in the leaf of a plant?
A
- Photosynthesis
- Gaseous exchange (to facilitate photosynthesis and respiration)
- Transport
- Protection
13
Q
The leaf is an organ of …
A
Photosynthesis
14
Q
What is the ileum?
A
The ileum is the region of the small intestine where digestion is completed and where most absorption of the products of digestion occurs.
15
Q
There is a vast surface area for digestion and absorption in the ileum provided by …
A
- Folds in the inner surface of the intestinal wall
- Projections called villi (singular: villus) that are present on the folded surface of the wall
- Microscopic projections called microvilli on the cell-surface membranes of columnar epithelial cells that line the villi.
16
Q
What is the mucosa?
A
This is the layer in contact with the food in the gut lumen
17
Q
What is the function of columnar epithelium tissue (within the mucosa)?
A
- This layer has column-shaped cells and lines the intestine.
- On their free surfaces the cells have microvilli, forming a brush border.
- Since digestive enzymes are bound to the membrane of the microvilli, this provides a huge surface area for digestion and for the absorption of the products of digestion.
- Some substances are taken up partly by diffusion and partly by active transport; others are taken up by pinocytosis.
- There are numerous mitochondria to aid active transport.
- The cells of the epithelium are short lived.
18
Q
What is the function of goblet cells (within the epithelium)?
A
- These cells secrete mucus.
- Mucus is slimy.
- Mucus provides a slimy protective layer.
- It protects the epithelium from the action of digestive enzymes
- and lubricates the lining as solid material is pushed along, facilitating the movement of food.
19
Q
What is the function of villi (within the mucosa)?
A
- These finger-like projections increase the surface area for the absorption of the products of digestion.
- The villi contain blood capillaries into which amino acids and monosaccharides are absorbed, and lacteals (blind-ending lymph vessels) into which fats are absorbed.
20
Q
Absorption Definition
A
Taking soluble molecules into the body
21
Q
Assimilation Definition
A
Incorporating absorbed molecules into body tissues
22
Q
What is the function of Crypts of Lieberkühn (within the mucosa)?
A
- These intestinal glands are found at the bases of the villi.
- The cells along the sides secrete mucus.
- The cells [stem cells] lining the bottom of the crypts are in a state of continuous division; new cells are continuously being pushed up by the division of cells deeper down.
- After a life of several days within the epithelium, the cells are pushed to the tips of the villi where they are sloughed off.
- Paneth cells are also present at the base of the crypts.
- Their function is to defend the actively dividing cells against microbes in the small intestine.
23
Q
What is the function of the muscularis mucosa?
A
• The muscle fibres contract to cause movement of the villi, so improving contact with the products of digestion in the gut lumen.
24
Q
What is the function of the submucosa?
A
- The submucosa contains blood vessels, including venules of the hepatic portal vein (carrying blood containing the digested food products to the liver) and lymphatic vessels, supported by connective tissue.
- The role of the submucosa is to transport the absorbed food products.
25
What is the function of the muscularis externa?
* The muscularis externa consists of circular muscle (innermost) and longitudinal muscle.
* Contractions of longitudinal muscle causes pendular movement of the gut while contraction of circular muscle may result in local constrictions, both of which churn and mix the food.
* Coordinated contractions of the circular muscle push food along the gut by peristalsis.
26
What is the function of the serosa?
This outer layer of connective tissue serves to protect and support the gut.
27
Knowledge check 57
| Explain why mucus is needed to protect the cells lining the ileum from protein-digesting enzymes.
Because the cell-surface membranes of the epithelial cells are partly composed of proteins (e.g. involved in facilitated diffusion and active transport.)
28
Knowledge check 58
| State one way in which the ileum is adapted to churn the food.
Contraction of longitudinal muscle causes pendular movements, while contraction of circular muscle causes local constrictions.
29
Vascular bundles (veins) in leaves are composed of ...
Xylem vessels
| Phloem sieve tubes
30
What is the structure of a leaf?
Structurally, the leaf consists of epidermal layers either side of a middle layer of mesophyll and vascular tissues.
```
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Xylem
Phloem
Lower epidermis
```
31
Exam Tip
| Remember that only plant cells with (blank) can photosynthesise.
Chloroplasts
32
Knowledge Check 59
| Explain how the palisade mesophyll is adapted to carry out its function.
Palisade cells lie towards the upper section of the leaf towards the source of light; they are cylindrical, so reducing the number of light-absorbing cell walls; they are packed with chloroplasts, which contain photosynthetic pigments. All of these features maximise light absorption for photosynthesis.
33
Knowledge Check 60
| What is the advantage to a plant of being able to control the opening and closing of stomata?
Opening during the day facilitates the uptake of CO2 for photosynthesis, while closing at night reduces the transpirational loss of water.
34
What is the function of the upper epidermis in a mesophytic leaf?
* The cells of the upper epidermis lack of chloroplasts since their role is protective.
* They secrete a waxy cuticle that provides waterproofing and reduces water loss.
35
What is the function of the palisade mesophyll in a mesophytic leaf?
* The palisade layer, in the upper half of the leaf, has layers of tightly packed cells, each with abundant chloroplasts.
* It is adapted for maximal light absorption.
* This is the main photosynthetic region of the leaf.
36
What is the function of the spongy mesophyll in a mesophytic leaf?
* The mesophyll in the lower half of the leaf contains large air spaces.
* Gaseous exchange between these air spaces and the atmosphere can take place via numerous pores (stomata).
* Spongy mesophyll cells also contain chloroplasts and are photosynthetic.
37
What is the function of xylem vessels in a mesophytic leaf?
• Xylem vessels supply the leaf with water and inorganic ions.
38
What is the function of phloem sieve tubes in a mesophytic leaf?
• Phloem sieve tubes translocate sugars (sucrose) produced in photosynthesis away from the leaf.
39
What is the function of stomata in a mesophytic leaf?
* The lower epidermis contains numerous stomata, which allow gaseous exchange.
* They also allow water vapour to diffuse easily out of the leaf.
* Each stoma (singular of stomata) is surrounded by a pair of guard cells, which close at night and so water loss by transpiration is minimised.
40
What is the function of the lower epidermis in a mesophytic leaf?
* The cells lack chloroplasts.
* The waxy cuticle secreted on the lower surface is thinner than that on the upper surface since it is not exposed directly to the Sun.
41
What do the upper and lower epidermis protect the leaf from?
1. Damage
2. Infection
3. Dehydration
42
The upper and lower epidermis are ...
Colourless
43
Stomata are (blank) during the day
Open
44
Name two transport tissues in the leaf
Xylem
| Phloem
45
What is the alimentary canal?
The alimentary canal is the part of the digestive system that forms the long hollow tube that runs from the mouth to the anus.
46
What different types of tissue does the leaf contain?
Epidermal tissue
Mesophyll tissue
- Palisade mesophyll tissue
- Spongy mesophyll tissue
Vascular tissue
- Xylem tissue
- Phloem tissue
47
What are the names of the tissue layers in the leaf in chronological order?
```
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Xylem
Phloem
Lower epidermis
```
48
Identify the gas exchange surface in leaves
The cell surface membrane of spongy mesophyll cells
49
What types of tissue does the ileum contain?
Epithelial tissue
Contractile tissue (muscle)
Blood tissue
Connective tissue
50
What are the adaptations of columnar epithelial cells?
* On their free surface the cells have microvilli, forming a brush border.
* Digestive enzymes are bound to the membrane of the microvilli.
* These adaptations provide a large surface area for digestion and for the absorption of the products of digestion.
* Numerous mitochondria are present to provide ATP for active transport of some digested food products.
51
Name the organs present in the digestive system
```
Ileum
Mouth
Oesophagus
Stomach
Pancreas
Liver
Colon
```
52
What two types of cell are present in mesophyll tissue?
Palisade mesophyll cells
| Spongy mesophyll cells
53
What is the serosa?
A thin outer layer of connective tissue.
54
What is the muscularis externa?
Contractile tissue consisting of an outer layer of longitudinal muscle and an inner layer of circular muscle.
55
What is the submucosa?
This region is largely composed of connective tissue and contains many blood vessels and lymphatic vessels.
56
What is the muscularis mucosa?
This thin layer of muscle lies between the submucosa and the mucosa.
57
How does the muscularis mucosa move the villi?
* Small strands of muscle extend from the main muscularis mucosa layer up through the mucosa into each villus.
* Contractions of these strands help to produce the characteristic 'wafting' movement of the villi.
58
Draw a villus
Textbook pg 112
59
Draw a simple diagrammatic cross section of the ileum
Textbook pg 111
60
How does digestion occur in the ileum?
1. Many digestive enzymes are secreted into the gut lumen.
| 2. Many digestive enzymes are bound to the cell surface membrane of ileum epidermal cells (columnar epithelium cells).
61
Lacteals are part of the ...
Lymphatic system
62
How are monosaccharides and amino acids absorbed into the capillary network within the villi?
The absorption of some products involves both active transport and (facilitated) diffusion, involving protein carrier molecules.
* Monosaccharides (e.g. glucose) and amino acids are taken into the epithelial cells by active transport.
* Once there, they can diffuse into the capillary network (by facilitated diffusion) due to the concentrations that can build up in the cells.
* The first stage (active transport) is needed as the molecules are being moved against the concentration gradient.
* The second stage (facilitated diffusion) is needed as monosaccharides and amino acids are polar (hydrophilic) and cannot pass through the hydrophobic centre of the phospholipid bilayer unaided.
63
What is a lacteal?
A lacteal is a blind-ending lymph vessel
64
How are proteins and some other substances absorbed into the capillary network within the villi?
• Pinocytosis
65
What is the absorptive surface in the ileum?
The columnar epithelium, with microvilli, on the villi of the mucosa layer.
66
Crypts of Lieberkühn possess ...
Stem cells
Paneth cells
Goblet cells
67
What is the role of stem cells in crypts of Lieberkühn?
To produce new epithelial cells
68
The waxy cuticle produced is ...
Transparent
69
How are lipids absorbed into lacteals within the villi?
* Lipid soluble products such as glycerol and fatty acids can simply diffuse into the cells lining the villi.
* The lipids will diffuse out of the cell, through the tissue fluid and into the lacteal.
* Lipids are transported out of the villi by lacteals.
70
What is the role of blood capillaries and lacteals within the villi of the mucosal layer?
Transportation of the products of digestion
71
Give an example of pinocytosis in the ileum
In babies, antibodies (proteins) can pass from breast milk into their blood system without being digested.
72
Draw a diagram of a leaf
Textbook page 114
73
What are villi?
Villi are finger-like projections of the wall of the mucosa
74
What are microvilli?
Microvilli are projections of the cell-surface membrane of ileum epidermal cells (columnar epithelial cells) lining the mucosa.
75
Guard cells are unusual for epidermal cells as they contain ...
Chloroplasts
76
What are the adaptations of the palisade mesophyll layer?
1. Occurs immediately below the upper epidermis, the surface of the leaf that receives the most light (in order to maximise exposure of light to the palisade cells).
2. The palisade cells are arranged regularly and are tightly packed (in order to pack in as many cells as possible).
3. Each cell has many chloroplasts to maximise photosynthesis.
4. The chloroplasts often accumulate at the top of each palisade cell in order to receive as much light as possible and maximise photosynthesis.
5. Depending on the species, there may be one or more layers of palisade cells in the palisade mesophyll.
6. The large vacuole in palisade cells helps the light to pass down through the layers with minimum shading.
7. Palisade cells are arranged perpendicular to the upper epidermis, therefore light has fewer cell walls/membranes to pass through.
8. Palisade cells are arranged perpendicular to the upper epidermis, maximising the incident light on each individual cell.
9. Palisade cells are arranged perpendicular to the upper epidermis, therefore sugars moving to the phloem have to pass through fewer cells, as do gases diffusing to and from the intercellular air spaces.
77
How is the large surface area of the leaf an adaptation for photosynthesis?
1. Provides more palisade cells in close proximity to the upper leaf surface
2. And also facilitates gas exchange with no cell being too far from a gas exchange surface
78
The leaf surface area is a compromise between ...
Maximising photosynthesis and minimising water loss
79
Past Paper Question - June 2017 Q8 b) AS1 (Revised Spec.)
Q8 b) Microscopy has enabled extensive study of the tissue layers of the ileum. Describe the structure and function of each of the tissue layers of the ileum. [9]
Q8 b) • mucosa layer is where absorption occurs
• villi are present which increase surface area
• microvilli increase surface area for diffusion
• epithelial cells have many mitochondria for active transport
• goblet cells produce mucus to protect mucosa/provide lubrication
• muscularis mucosa is a thin layer of muscle that controls movement of the villi which increases contact with digested food in the gut lumen
• villi have a rich network of capillaries which maintains diffusion gradient between lumen and blood
• submucosa contains blood and lymphatic vessels for transport
• muscularis externa consists of both longitudinal and circular muscles
causing pendular movements/peristalsis
• serosa is a thin outer layer of connective tissue – this provides
protection and support of the ileum
• lacteal for absorption of fatty acids and glycerol
• crypts of Lieberkühn/Paneth cells for antimicrobial action [9]
80
Past Paper Question - June 2016 Q3 c)i) AS1 (Legacy Material)
Q3 Photograph 1.3 shows a transverse section through part of a privet leaf (Ligustrum ovalifolium).
c) The cells in the main photosynthesising layer of these leaves are normally very tightly packed together.
i) Explain one advantage to the plant of this arrangement. [1]
Q3 c)i) Maximise light absorption/ less chance of light passing through leaf without striking a chloroplast/ more chlorophyll for light absorption. [1]
81
Past Paper Question - June 2016 Q3 c)ii) AS1 (Legacy Material)
Q3 Photograph 1.3 shows a transverse section through part of a privet leaf (Ligustrum ovalifolium).
c) The cells in the main photosynthesising layer of these leaves are normally very tightly packed together.
ii) In photograph 1.3 the cells of this layer do not appear to be very tightly packed. Suggest a reason for this appearance. [1]
Q3 c)ii) Some cells lost/torn due to preparation; [1]
82
Past Paper Question - January 2014 Q6 c)i)+ii) AS1 (Legacy Material)
Q6 c) Some people are intolerant of gluten in the diet. This is the basis of the condition known as coeliac disease. One of the proteins in gluten, gliadin, triggers an immune response in sufferers which results in damage to the lining of the ileum. This damage is often patchy and does not affect the whole ileum.
Sections of the ileum mucosal layer from a normal individual and from a coeliac sufferer are represented in the diagram below.
i) Describe the effect of coeliac disease on the structure of the ileum. [1]
ii) Coeliac sufferers are often nutrient-deficient. With reference to the damage caused to the ileum, suggest an explanation for this. [2]
(Go do this past paper)
Q6 (c) (i) Villi are flattened/destroyed; [1]
ii) The surface area of the ileum is reduced;
Resulting in less effective absorption of nutrients; [2]
83
Past Paper Question - January 2014 Q6 c)iii) AS1 (Legacy Material)
Q6 c) Some people are intolerant of gluten in the diet. This is the basis of the condition known as coeliac disease. One of the proteins in gluten, gliadin, triggers an immune response in sufferers which results in damage to the lining of the ileum. This damage is often patchy and does not affect the whole ileum.
Sections of the ileum mucosal layer from a normal individual and from a coeliac sufferer are represented in the diagram below.
iii) When investigating the ileum of a potential sufferer for signs of coeliac disease, several biopsies (tissue samples) are taken, each from a different region of the ileum. Suggest why. [1]
Q6 c)iii) To improve the chances of finding the symptoms (since they are patchy) [not to improve reliability]; [1]
84
Past Paper Question - June 2014 Q1 a) AS1 (Legacy Material)
Q1 The wall of the ileum is made up of several tissue layers, as shown in the diagram below.
Between each villus is a region containing some actively dividing cells called stem cells. These are able to divide and develop into a variety of cell types, each of which becomes a component of the tissue layer labelled X in the diagram.
a) State the name of tissue layer X. [1]
(Go do this past paper question)
Q1 a) Mucosa; [1]
85
Past Paper Question - June 2014 Q1 b) AS1 (Legacy Material)
Q1 The wall of the ileum is made up of several tissue layers, as shown in the diagram below.
Between each villus is a region containing some actively dividing cells called stem cells. These are able to divide and develop into a variety of cell types, each of which becomes a component of the tissue layer labelled X in the diagram.
b) Paneth cells and goblet cells are two types of cell produced by the stem cells. State the functions of Paneth cells and goblet cells in the ileum. [2]
Q1 b) Paneth cells produce anti-microbial substances/to protect stem cells;
goblet cells produce mucus; [2]
86
Past Paper Question - January 2012 Q9 Section B AS1 (Legacy Material)
Q9 In complex organisms, cells are organised into tissues which are then organised into organs. The ileum is an example of an organ. Describe the structure and function of the different tissue layers in the ileum and, where appropriate, their constituent cells. [13]
Quality of written communication [2]
Q9 Any thirteen points
• on the outside, the serosa provides a supportive/protective layer
• inside this is the muscularis externa
• containing both longitudinal and circular muscles
• which are responsible for pendular movements/local constrictions which mix food and enzymes together
• and for peristalsis which moves food along the ileum
• inside this is the submucosa
• which contains blood vessels/lymphatic vessels/connective tissue
• the muscularis mucosa is involved in movement of the villi
• which improves contact between the absorbing surfaces and the digested food
• the mucosa is the innermost layer/in contact with food
• (it is deeply folded into) villi to increase the surface area/nutrient absorption
• in the centre of each villus there is a lacteal into which the fats are absorbed
• and a network of blood capillaries into which monosaccharides/amino acids are absorbed
• (between) the villi are the crypts of Lieberkühn
• where Paneth cells are responsible for producing new epithelial cells/have an anti-microbial function to protect the stem cells at the base of the crypts
• the surface of the villi is covered with columnar epithelium
• epithelial cells have microvilli to increase surface area/absorption
• and mitochondria to provide ATP/energy for active transport
• goblet cells secrete mucus
• which lubricates the ileum/protects the cells from enzyme action [13]
Quality of written communication [2]
87
Past Paper Question - June 2012 Q6 a)+b) AS1 (Legacy Material)
Q6 Photograph 1.6 is an electron micrograph showing several cells from the mesophyll layer of a spinach leaf. A box has been drawn round one cell, identified as cell A, as well as parts of its neighbouring cells.
a) In the space below, draw a diagram of cell A as shown in the box in the photograph. Your drawing should indicate the structures visible within the cell. It should also include the outlines of the various neighbouring cells (but should not include any detail of structures in these extra cells).
Label at least four structures in your diagram.
Drawing [3]
Labels [2]
b) Identify one piece of evidence in the photograph to support each of the following statements. [2]
• The cells shown are probably from the spongy mesophyll layer.
__________________________________________________________________________
__________________________________________________________________________
• The cells shown are not from the epidermis.
__________________________________________________________________________
__________________________________________________________________________
(Go do this past paper question)
Q6 a) Drawing marks awarded for the following points:
Shape of cell accurate and recognisable as cell A in the photograph;
cell and its neighbours in proportion to each other (e.g. where cells touch wall of neighbouring cell relevant length compared to cell A, chloroplast appropriate size);
appropriate organelles shown (e.g. peripheral cytoplasm, chloroplasts, possible nucleus, vacuole); [3]
Labels: any four from
• cell wall
• cell membrane
• nucleus
• chloroplasts
• thylakoids
• stroma
• intercellular spaces
• vacuole
• tonoplast
• cytoplasm
• middle lamella
[1/2 mark each]
b) Spongy mesophyll: intercellular air spaces evident/cells loosely packed;
Not epidermis: epidermal cells would not have chloroplasts/chloroplasts present in these cells/not a tightly packed layer of cells;
88
Past Paper Question - June 2011 Q4 a)+b) AS1 (Legacy Material)
Q4 Photograph 1.4 is a section through part of the ileum.
(a) Identify the structures labelled A to E.
A __________________________________________
B __________________________________________
C __________________________________________
D __________________________________________
E __________________________________________ [5]
(b) Suggest an interpretation for the area labelled F.
____________________________________________________________________
____________________________________________________________________ [1]
(Go do this past paper question)
Q4 a) A: Muscularis mucosa [NOT just muscle];
B: crypt Lieberkühn/Paneth cells/stem cells;
C: goblet cell;
D: columnar epithelium [NOT just epithelium];
E: mucosa [NOT villus]; [5]
(b) This is a surface view of a villus/section of epithelium layer (surrounding villi are shown sectioned); [1]
89
Past Paper Question - June 2011 Q4 c) AS1 (Legacy Material)
| Q4 c) Describe the role of the lacteal within each villus of the ileum. [1]
Q4 c) The lacteal absorbs lipids/fatty acids and glycerol; [1]
90
Past Paper Question - June 2013 Q6 a)i+ii) AS1 (Legacy Material)
Q6 a) The following diagram shows a transverse section through part of a mesophytic leaf. Six tissues are labelled A-F.
i) Using the appropriate letter from the diagram, identify the tissue in which each of the following processes happen:
* maximum absorption of light
* diffusion of gases
* transport of water [3]
ii) State the role of the cuticle. [1]
(Go do this past paper question)
[Textbook Chapter 6 Exam Question 2, page 116-117]
Q6 a)i)
B;
C (accept D);
E; [3]
ii) To reduce/minimise water loss by evaporation/transpiration; [1]
91
Exam Question - CCEA Biology for AS Level 1st Edition Textbook
Past Paper Question from AS1 June 2011
Q2 The photograph below is a section through part of the ileum.
b) Suggest an interpretation for the area labelled F. [1]
[Photograph shown is present in camera roll.]
Q2 b) This is a surface view of a villus/section of epithelium layer (surrounding villi are shown sectioned); [1]
92
Exam Question - CCEA Biology for AS Level 1st Edition Textbook
Past Paper Question from AS1 June 2010
Q3 The diagram below shows the tissues present in a mesophytic leaf.
The leaf is an organ with adaptations for maximising photosynthesis while minimising transpiration.
Describe these adaptations for:
* Maximising photosynthesis [3]
* Minimising transpiration [2]
[Photograph shown is present in camera roll.]
Q3 Maximising photosynthesis: Any three from
• transparent upper epidermis allows light through to underlying palisade cells
• palisade mesophyll cells are tightly packed (to facilitate light absorption)
• palisade cells are densely packed with chloroplasts/chloroplasts are accumulated at the top of the palisade cells
• spongy mesophyll consists of loosely packed cells/creates air spaces/ facilitates gas exchange
• xylem provides water (for photosynthesis)
• stomata allow gas exchange
• thin to reduce distance for gas exchange
• large surface area to absorb more light [3]
Minimising transpiration: Any two from
• stomata located on lower surface/away from source of radiation (heat)
• epidermal cells are covered with a (waterproof) waxy cuticle
• stomata close at night/during times when there is excessive water loss
• guard cells control closing of stomata [2]
93
CCEA AS Unit 1 Student Guide - Questions and Answers
Question 16 - The leaf (page 95)
b)i) State the role of the cuticle. [1]
ii) The guard cells have a dual role in the leaf. Explain this role. [2]
b) i) The waxy cuticle reduces the loss of water by evaporation from the surface of the leaf. [1]
ii) Guard cells open during the day to allow gases to diffuse in and out of the leaf (CO2 in for photosynthesis) [1] and close at night to prevent excessive transpirational loss of water [1].
94
Capillaries and lacteals in villi are surrounded by ...
Tissue fluid
95
Give an example of a plant which has adapted to arid conditions and explain their adaptation
Cacti
Needle shaped leaves decrease the surface area across which water loss can occur
96
What are the adaptations of the spongy mesophyll layer?
• The loose and irregular arrangement of these cells leads to the formation of intercellular air spaces (producing a large gaseous exchange surface) that encourage the diffusion of gases (carbon dioxide and oxygen) for gas exchange necessary for photosynthesis and respiration.
97
Phloem sieve tubes transport sugars, usually sucrose, produced in photosynthesis away from the leaf to ...
Plant storage regions such as bulbs or tubers (where it can be converted to starch) or to actively growing regions where it is used in respiration.
98
Why is the waxy cuticle on the lower epidermis thinner than that on the upper epidermis?
Less transpiration tends to occur though the lower epidermis
99
When turgid, the guard cells ...
Expand and open the pore of the stoma, thereby facilitating gas exchange.
100
When less turgid, the guard cells ...
Become flaccid and shrink, closing the pore and thereby reducing water loss.
101
Stomata are (blank) during the day and (blank) at night.
Open
| Closed
102
Why are stomata closed at night?
To reduce water loss.
During darkness, leaf metabolic activity is reduced, with only respiration taking place and there is usually enough oxygen within the leaf to allow respiration to take place even with the stomata closed.
103
Why are stomata open during the day?
Despite evaporation losses being greater during the day when it is warmer, the stomata need to remain open to allow the gases involved in photosynthesis and respiration to enter and leave.
104
During darkness, leaf metabolic activity is ...
Reduced
105
Give an example of a plant species with stomata on both leaf surfaces
Grasses
106
Give an example of a plant species with stomata on the upper leaf surface only
Water lilies
