Digestive system- Sample Qs

Diagram 6 shows the human digestive system. (a) Based on Diagram 6 state the adaptation characteristics of structure B for nutrient and also what happens to the excess amino acids in the body. (4 marks)

(b) Draw and label a cross-section of a villus.
Explain how villus is linked to organ A in the transport of nutrients and also what happens to the excess amino acids in the body. (6 marks)

(c)Describe the digestive actions that take place in the

(i) mouth
(ii) stomach
(iii) small intestine

Explain the roles of the glands secretion, enzyme involved in these digestive process.
(10 marks)

Suggested Answer:

(a)Adaptation of small intestine :
· the great length
· the folded inner surface
· Has a large surface area because it has a lot of finger-like projections on its membrane called microvilli. // Microvilli help increase the absorption of digested food.
· A villus is supplied with a network of blood capillaries which aids in the absorption and transport of digested food. (nutrients)

(b)

· Each villus has blood capillaries that transport nutrients such as glucose and amino acids.

· The blood capillaries converge to form the hepatic portal vein which leads to the liver

· Excess amino acids cannot be stored in the body and are broken down in the liver // deamination

· During deamination, urea and the common nitrogeneous waste product is produced and transported to the kidneys to be excreted.


(c) Mouth
· Food is chewed and broken up into smaller pieces by the teeth.
· The small pieces of food have a larger surface area for the saliva (enzyme) to act upon.
· Salivary gland secretes saliva that is alkaline and contains salivary amylase (ptyalin).
· After the food has been thoroughly chewed and mixed with saliva, the tongue starts the process of swallowing by pushing the bolus (small mass of chewed food).
· Saliva also softens and increases the water content of the food.
· In mouth, only starch is digested. Starch is hydrolysed by amylase into maltose.
Starch + Water -----Amylase ------- Maltose

Stomach
· Secretes gastric juices contains hydrochloric acid and enzyme (rennin and pepsin)
· Hydrochloric acid kills microorganisms and stops the activity of salivary amylase, which functions optimally at the near-neutral pH of saliva and promotes the activity of pepsin.
· Pepsin is a hydrolytic enzymes that acts on protein to produce peptides

Protein + Water--------- pepsin -------- Peptone + polypeptide

Rennin changes caseinogens to casein. Casein is then digested by pepsin

Caseinogens ------- Rennin -------- Casein

Ileum (small intestine)
· There are some digestive glands on small intestine. All these enzymes need an alkaline medium function
· There are 5 types of enzymes produced :
1. Erypsin (peptidase) – hydrolysis of peptide to amino acids
2. Sucrase - hydrolysis of sucrose to fructose and glucose
3. Maltase - hydrolysis of maltose to glucose
4. Lactase - hydrolysis of lactose to glucose and galactose
5. Entrokinase – Activates trypsinogen to trypsin in the
duodenum

Type of nutrition-Sample QS

Diagram shows organism, P, Q and R.

(a) (i) Describe the type of nutrition in P and Q.
[4 marks]

(ii) Explain one similarity and four differences between the alimentary canal of Q and R.
[6 marks]

Suggested Answer

(a)(i)

P: Autotrophic that enables to produce their own food by photosynthesis process using simple inorganic substances to form complex organic substances
Q: Heterotrophic unable to produce their own food, it depends to others organism for food

(ii)Both contain anaerobic bacteria and protozoa in their alimentary canal for digestion of cellulose

Plasma membrane- Sample QS

The figure shows a fluid mosaic model of the plasma membrane

(a) Explain the functions of the structures X, Y and Z in the movement of substances across the plasma membrane
[4 marks]

(b) All movements of substances have to pass through a plasma membrane. Explain why the plasma membrane is known as a semi permeable membrane
(6 marks)

Suggested Answer:

(a)
· Structure X allows hydrophobic molecules which can dissolve in lipids such as fatty acids, glycerol, steroid hormones, vitamins A, D, E and K to move in and out of the cell.

· Structure Y allows bigger molecules which do not dissolve in lipids like glucose and amino acids to move in and out of the cell.

· Structure Z allows small charged molecules to move in and out of the cell.

(b)

· The plasma membrane is known as a semi permeable membrane because it only allows the passage of certain molecules and limits the passage of other molecules.
· It consists of two layers of phospholipids with protein molecules scattered in them
· Molecules that can pass through the plasma membrane easily are those that can dissolve in lipid and small uncharged molecules.
· Molecules which cannot move through the plasma membrane but require proteins include large molecules that do not dissolve in lipid and small charged molecules.
· Channel protein does not require the binding of a molecule and conformational change to open.
· Channel protein allows molecules to steadily diffuse across the membrane through diffusion.
· However a carrier protein allows specific molecules to cross the cell membrane by undergoing a conformational change upon the binding of the molecule.
· The conformational change opens a hole through which the molecule can enter or leave a cell.

Interaction between organism-Sample Qs

It is Question 7 (a) Paper 2 SPM 2009....and the suggested answer!

Name and describe the interaction shown in Diagram 7.1. [ 4 Marks]

Parasitism.....[ 1 mark]

-The organism (Rafflesia sp)

-which will benefit by living and obtaining nutrients from its host which is living and

-cause harm and weaken their host in the process.

Nitrogen Cycle-Sample Qs

Look at the scanned Qs from Paper 2 SPM 2009

and please go through the suggested answer....

-Nitrogen fixing bacteria in root nodules of leguminous plats use nitrogen in the air to make nitrates.
-Nitrates then are absorbed by plants to make protein
-When animals eat plants the protein is transferred to animals
-When plants and animals die, and excretory nitrogenous substances are decomposed by decaying bacteria. It breaks them down to ammonia
-Nitrifying bacteria converts ammonium compounds
-Nitrifying bacteria changes nitrit to nitrate
-Denitrifying bacteria converts nitrates to nitrogen.