Tissues and Organs

Question 1

1. What is a tissue?

Answer 1

A group of cells (often very similar in shape) that work together to carry out the same function

Question 2

2. What is an organ?

Answer 2

A group of tissues that work together to carry out one or more functions.

Question 3

3. What is an organ system?

Answer 3

A group of organs that work together e.g. digestive system.

Question 4

4. Name the 5 layers of the ileum, visible in a cross section diagram (FROM THE OUTSIDE IN)

Answer 4

serosa Muscularis externa Submuscosa Muscularis mucosa Mucosa

Question 5

5. What is the function of the serosa?

Answer 5

An outer layer of connective tissue which provides a very thin protective and supportive lining for the alimentary canal.

Question 6

6. What is the function of the muscularis externa?

Answer 6

Peristalsis: Contractions of the longitudinal muscles cause pendular movements. Contractions of the circular muscles cause local constrictions and help push food along the gut in a series of peristaltic waves

Question 7

8. What is the function of the muscularis mucosa?

Answer 7

This thin layer of muscle has small strands of muscle extending upward into each villus, and when they contract they waft the villi. This movement of villi improves contact with the digested food.

Question 8

7. What is the function of the submucosa?

Answer 8

This layer is mainly composed of connective tissue but also contains many blood vessels and lymphatic vessels to transport absorbed food products.

Question 9

9. What is the function of the mucosa?

Answer 9

It is the layer in contact with digested food in the gut lumen. It is lined with columnar epithelial cells and it has a hugely increased surface for absorption due to villi and microvilli on the folds

Question 10

10. Label the 5 layers of the ileum shown in the diagram

Answer 10

cross section- see KO

Question 11

11. What are the cells called that line the external surface of the villi?

Answer 11

Columnar epithelial cells.

Question 12

12. Describe and explain some of the adaptations of the columnar epithelial cells for the absorption of digested food.

Answer 12

1. Their surtace areas greury increased by presence of numerous microvilli (a brush border) for absorption of digested food 2. They are rich in mitochondria, the sites of aerobic respiration, where ATP is made. ATP is needed for active transport of glucose and amino acids into the columnar epithelial cells. 3. They have an increased number of membrane protein carriers for facilitated diffusion

Question 13

13. How are digested food molecules absorbed into the villi and then on into the blood?

Answer 13

• Glucose & amino acids are taken into the epithelial cells by active transport and from there, into the capillaries by facilitated diffusion. (The hepatic portal vein then takes them to the liver) * Fatty acids and glycerol move into the epithelial cells by facilitated diffusion, they then move into the lacteals for transport initially in the lymphatic system * Some fats are taken up by pinocytosis

Question 13

14. What are goblet cells and where are they found?

Answer 13

Goblet cells are found dotted between the columnar epithelial cells. They secrete mucus, which acts as a slimy protective layer that lubricates the lining of the gut, facilitates movement of food along it and protects the epithelial cells from digestive enzymes

Question 14

15. What are Crypts of Lieberkuhn and where are they found?

Answer 14

Crypts of Lieberkuhn are intestinal glands found in the tissue between villi. Cells at the bottom of the crypts are continually dividing by mitosis, producing new cells that constantly move up the villi to replace old ones

Question 14

17. Label the structure of the villus.

Answer 14

see notes

Question 14

16. What are Paneth cells and where are they found?

Answer 14

They are found at the base of the crypts and have an antimicrobial function, protecting the actively dividing cells.

Question 15

18. Describe the upper epidermis tissue layer in a leaf

Answer 15

A transparent protective layer, without chloroplasts and covered with a waxy cuticle which reduces water loss.

Question 16

19. The palisade mesophyll layer is the primary photosynthesising region in the leaf. Describe it’s adaptations to harvest light energy.

Answer 16

1. Found immediately beneath the upper epidermis so receives the most light 2. Palisade cells are tightly packed in a regular arrangement, to pack as many cells in as possible and each cell is densely packed with chloroplasts. 3. Palisade cells lie perpendicular to the upper epidermis and the large vacuole helps light to pass down through them to layers below

Question 17

20. Describe the arrangement of the cells in the spongy mesophyll layer and how this is advantageous for the process of gas exchange

Answer 17

• The cells are loosely packed and irregularly arranged, leading to the formation of intercellular air spaces * These air spaces encourage the diffusion of gases for gas exchange * Gas exchange occurs via diffusion through the cell surface membrane of the spongy mesophyll cells which provide a large exchange surface due to their loose arrangement

Question 18

21. What is the role of the vascular tissue?

Answer 18

• xylem vessels transport water and mineral ions up to the leaves * phloem sieve tubes transport sugars, mainly sucrose, produced during photosynthesis, away from the leaves and to storage areas

Question 19

22. Describe the lower epidermis.

Answer 19

• Stomata are present, their opening and closing being controlled by guard cells * Guard cells contain chloroplasts * When the guard cell is turgid, the stoma pore opens facilitating gas exchange. When less turgid, the stoma closes, reducing water loss * A thin waxy cuticle is present.

Question 20

23. Label the cross section of a mesophytic leaf.

Answer 20

See notes