(U1) Tissues And Organs

Question 1

What is the alimentary canal?

What are the 5 tissue layers within it?

Explain each’s function

Answer 1

1. a long hollow tube from the buccal cavity to the rectum
2. From outside to inside:

• serosa: connective tissue; protective and supportive lining
• musclaris externa: pushes food by peristalsis
• submucosa: connective tissue containing blood and lymphatic vessels
• musclaris mucosa: moves villi in the mucosa (wafting), increasing contact with digested food
• mucosa: increased SA with many villi and microvilli

Question 2

Describe the process of peristalsis in the musclaris externa (3)

Answer 2

• longitudinal muscle contract causing pendular movement
• circular muscle contractions cause local constrictions
• this pushes food along

Question 3

How are villi structured? (i.e. cells etc.) (6)

Answer 3

• columnar epithelial cells with microvilli - outer lining
• between many are goblet cells
• crypts of Lieberkühn between villi
• paneth cells on outer part of each crypt
• network of internal blood capillaries
• lacteal

Question 4

What is the effect of the different parts of villi? (i.e. cells etc.) (6)

Answer 4

1. columnar epithelial cells with microvilli:

• microvilli increase SA for active transport
• cells contain many mitochondria for ATP production
• microvilli also help accommodate enzymes held in the cell membrane
• also site of pinocytosis

2. Goblet cells:

• secrete mucus needed for lubrication for smooth movement of food
• also needed for protection of the lining against hydrolytic enzyme digestion

3. Paneth cells:

• produce antimicrobial substances

4. Capillary network:

• absorbs digested food molecules

5. Lacteal:

• absorbs fatty acids and glycerol into the lymphatic system

6. Crypts of Lieberkühn:

• cells constantly divide and move up the villus to replace cells being worn away at the top

Question 5

How are mesophytic leaves structured? (i.e. cells, tissues etc.) (7)

Answer 5

1. waxy cuticle
2. upper epidermis
3. palisade mesophyll layer (with palisade cells)
4. spongy mesophyll layer (with spongy mesophyll cells and intercellular air spaces)
5. Vascular tissue in spongy mesophyll layer:

• xylem vessel
• phloem companion cell
• phloem sieve tube

6. Lower epidermis (including guard cells and stomata)
7. Waxy cuticle

Question 6

How are leaves adapted for max photosynthesis and min transpiration?

with regards to SA (2)

Answer 6

large SA:

• provides more palisade cells in close proximity to the upper leaf surface (increasing light absorption)
• also facilitates gas exchange; no cell far from a gas exchange surface

Question 7

How are leaves adapted for max photosynthesis and min transpiration?

with regards to the upper epidemis (2)

Answer 7

Upper epidermis with waxy cuticle:

• no chloroplasts; light passes to palisade layer with min shading
• hydrophobic waxy cuticle limits cuticular water loss

Question 8

How are leaves adapted for max photosynthesis and min transpiration?

with regards to the palisade layer (4)

Answer 8

Palisade mesophyll:

• arranged perpendicularly for max no. of cells (increased light absorption)
• palisade cells densely packed with chlorophyll (increased light absorption)
• large vacuole allows light to pass through with minimal shading (Increased light absorption in spongy cells)
• due to the arrangement of cells, sugars moving to the phloem have to pass through fewer cells, same for gases diffusing to and from the intercellular air spaces

Question 9

How are leaves adapted for max photosynthesis and min transpiration?

with regards to the spongy layer (3)

Answer 9

Spongy mesophyll layer:

• intercellular air spaces encourage diffusion of gases for gas exchange
• cells contain some chloroplasts for light absorption
• cells have large SA (rounded) for diffusion of gases

Question 10

How are leaves adapted

with regards to vascular bundles (2)

Answer 10

Vascular bundles:

• xylem carries water and inorganic ions to the leaves
• phloem sieve tubes transport sugars (sucrose) produced in photosynthesis from the leaf to storage regions or growing regions for respiration

Question 11

How are leaves adapted for max photosynthesis and min transpiration?

with regards to the lower epidermis (4)

Answer 11

Lower epidermis:

• thinner waxy cuticle due to less transpiration occurring (still limits transpirational water loss)
• stomata opened and closed by guard cells; open when turgid, closed when less turgid to restrict water loss
• guard cells contain chloroplasts for light absorption
• guard cells close stomata at night to minimise water loss