6.5.1 Functions of the Liver and Assimilation

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Transport of Nutrients by Circulatory System
1.   Glucose, amino acids, minerals, vitamins B and C are absorbed into blood capillaries of the villus and carried out of the small intestine to the liver by the hepatic portal vein.
2.   The hepatic portal vein transports the nutrients absorbed from the small intestine to the liver for processing and prepared for metabolic process or assimilation.
3.   Assimilation takes place in the cells where the nutrients are used to form complex compounds or structural components, for example, the transformation of amino acids to proteins.
4.   Glycerol and fatty acids as well as vitamins A, D, E and K are absorbed into the lacteal of the villus and transported out of the small intestine by the thoracic duct to the lymphatic system. The lymph is then transported by the thoracic duct to the subclavian vein. The lipid droplets and fat-soluble vitamins are then transported to all the cells via the blood circulatory system.

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Functions of the Liver
1.   Regulation of blood glucose levels
Convert excess glucose to glycogen for storage, and glycogen to glucose when the glucose level is low.
2. Storage of nutrients
   (a)  Excess glucose is converted into fats in the liver and later stored in other parts of the body.
   (b)  The liver also stores iron and fat soluble vitamins such as A, D, E and K.
3.   Deamination
Breaks down excess amino acid to ammonia in a process called deamination. Ammonia is then converted to urea and is excreted in the urine.
4.  Detoxification
The liver detoxifies blood by removing and metabolizing toxic substances.
5.  Production of bile
   (a)  Bile contains bile salts and bile pigments which are delivered to the duodenum.
   (b)  Bile emulsifies lipid droplets into tiny droplets. This increases the surface area of the action for the lipase.
6.   Synthesis of plasma proteins
  The liver is the site of plasma protein synthesis, for example, fibrinogen and prothrombin, which are vital blood clotting agents, are synthesized in the liver.

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1.   Assimilation is the process by which food materials after being absorbed are built up into complex constituents of the organism.
2.   Glucose
  ·  Glucose is oxidised in body cells during respiration to produce energy for various
   activities such as cell division.
  ·  Excess glucose is converted into glycogen and stored in the liver.
  ·  When the blood sugar level falls and the body needs energy, the stored glycogen is converted back into glucose.
3.   Amino Acids
  · Amino acids are absorbed by body cells to synthesise various types of proteins such as enzymes, antibody, plasma membrane and protoplasm.
  · Excess amino acids are broken down in the liver and converted into urea which is excreted in the urine through the process of deamination.
4.   Lipids
   · Lipids (fat droplets) are absorbed by body cells to build the plasma membrane and cholesterol.
   · Phospholipids are components of the plasma membrane.
   · Excess fat are stored in adipose tissue underneath the skin as reserve energy and around internal organ.
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6.5 Absorption and Assimilation of Digested Food

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6.5 Absorption and Assimilation of Digested Food
1.   Ileum is the major site of nutrient absorption.
2.   Soluble nutrients are absorbed by simple diffusion, facilitated diffusion or active transport.
Adaptive characteristics of the digestive system
1.   The wall of the small intestine is covered with epithelial cells that are specialized to complete the digestive process.
2.   The small intestine in adults is a long and narrow tube about 6 metre long, is the longest section of the alimentary canal.
3.   The small intestine contains small finger-like projections of tissue called villi which increase the surface area of the intestine and contain specialized cells that transport substances into the bloodstream. 
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4.   Specific feature of the villi:
(a)  there are numerous in number. This feature increases the internal surface area of the intestinal walls making available a greater surface area for absorption.
(b)  they have moist and thin wall, one cell thick, which enables a shorter diffusion path.
(c)  the epithelial cells contain microvilli which provide a large surface area for more rapid absorption.
(d)  contain network of blood capillaries for the absorption and efficient transport of digested food.
(e)  contain lacteals for more efficient absorption of fatty acids and glycerol into the blood stream. 

5.   The absorbed food substances are transported to the various body tissues or organs to be assimilated or to be stored for later use.
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6.4.2 Digestion in the Small Intestine

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6.4.2 Digestion in the Small Intestine

Digestion in the Small Intestine
1.   The small intestine consists of the duodenum, jejunum and the highly coiled ileum.
2.   The duodenum is the first part of the small intestine, receives chyme from the stomach and secretions from the gall bladder and pancreas.

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Digestion in the duodenum 
1.   Bile is an alkaline, greenish-yellow liquid produced in the liver and stored in the gall bladder. When stimulated, bile is transported from the gall bladder to the duodenum.
2.   Bile does not contain any digestive enzymes.
3.   Bile helps to reduce the acidity of the chyme and optimises the pH for enzyme action.
4.   Bile salts emulsify the lipids (fats) and break them up into tiny droplets, thus providing a larger surface area for digestion by enzymes (lipase).
1.   Pancreas secretes pancreatic juice which contains the enzymes pancreatic amylase, trypsin and lipase, transported by the pancreatic duct, to the duodenum.
2.   The optimum pH required for the action of enzymes in the pancreatic juice is between 7.2 and 8.2.
1.   In the duodenum, pancreatic amylase hydrolyses the starch to maltose. 

2.   Trypsin hydrolyses polypeptides into shorter peptide chains. 

3.   Lipase hydrolyses the lipids to glycerol and fatty acids.

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Digestion in the ileum
1.   Glands in the wall of the ileum secrete intestinal juice which contains digestive enzymes needed to complete the digestion of food.
2.   At the end of the digestive process, all carbohydrates are digested into monosaccharides such as glucose, fructose and galactose.
· Maltase hydrolyses maltose to glucose

· Sucrase hydrolyses sucrose to glucose and fructose

· Lactase hydrolyses lactose to glucose and galactose
3.   Proteins are digested into amino acids and lipids into fatty acids and glycerol.
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6.4.1 Human Digestive System

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6.4.1 Human Digestive System
1.      The human digestive system comprises of the alimentary canal which starts at the mouth and ends at the anus.
2.      The parts of the human digestive system are:
      (a) mouth
      (b) oesophagus
      (c) stomach
      (d) duodenum (first part of small intestine)
      (e) ileum (rest of small intestine)
      (f) large intestine (caecum, colon, rectum)

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Digestion in the mouth
1.      Digestion of food begins in the mouth.
2.      The chewing action breaks the food into smaller pieces. This makes it easier to swallow the food and increases the surface area for chemical digestion by enzymes.
3.      There are three pairs of salivary glands in the mouth to produce saliva.
4.      Saliva contains the enzyme salivary amylase which begins the hydrolysis of starch to maltose.
5.      The food particles are rolled into a small ball called bolus.
6.      During swallowing, the bolus enters the oesophagus

1.      The bolus moves along the oesophagus by a process called peristalsis, a series of wave-like muscular contractions along the oesophageal wall.
2.      Mucus secreted by the oesophagus wall to lubricate the passage of the bolus.
3.      When the cardiac sphincter relaxes, the bolus enters the stomach.

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Digestion in the stomach
1.      Gastric glands in the walls of the stomach secrete gastric juice.
2.      Gastric juice contains hydrochloric acid and the enzymes pepsin and rennin.
3.      Hydrochloric acid
(a) Creates an optimum pH (1.5-2.0) for the action of the enzymes pepsin and rennin.
(b) Stops the activity of salivary amylase.
(c) Kills bacteria that are present in the food.
4.      Pepsin hydrolyses the protein molecules into smaller polypeptides.

5.      Rennin coagulates milks by converting the soluble milk protein, caseinogen, into insoluble casein.

6.      The regular churning movements of the stomach mix up the gastric juice with food.
7.      The food remains in the stomach for 2 to 4 hours.
8.      The semi-liquid food is called chyme.
9.      The pyloric sphincter then relaxes. It allows the chyme to enter the duodenum, a little at a time.
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4.9.3 The Properties of Substances (Structured Questions)

Question 1:
Diagram 1.1 and Diagram 1.2 show an experiment to study the electrical conductivity of lead(II) bromide.

(a)(i) Based on Diagram 1.2, what is your observation on the needle of the ammeter? [1 mark]

(ii) What is the reading of the ammeter in Diagram 1.2? [1 mark]

(b) State the variables I this experiment.
  (i) Manipulated variable:
  (ii) Responding variable:
[2 marks]

(c) State one inference for this experiment. [1 mark]

(d) Lead(II) bromide is an ionic compound.
  State the operational definition for an ionic compound. [1 mark]

The pointer of the ammeter is deflected.

0.4 A

The state of the lead(II) bromide or chemical compound

The ammeter reading

Lead(II) bromide in the molten state can conduct electricity.

An ionic compound in the molten state will cause the pointer of the ammeter connected in a closed circuit to be deflected.

6.4 Food Digestion

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6.4 Food Digestion
1.   Digestion is the process that breaks down complex food substances into simpler, soluble molecules that are small enough for the body to absorb.

2.   Digestion breaks down
 (a) carbohydrates into glucose molecules,
 (b) proteins into amino acids, and
 (c) lipids into glycerol and fatty acids.

3.   Digestion involves both physical and chemical processes.

4.   Physical digestion
 (a) involves the breaking of large pieces of food into smaller pieces by chewing action of the teeth.
 (b) this action increases the surface area of the food particles for enzyme reaction.

5.   Chemical digestion
  Digestive enzymes break down of large complex food particles into simple soluble molecules by specific digestive enzymes in the presence of water. The process called hydrolysis.
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4.9.2 Proton Number and Nucleon Number (Structured Questions)

Question 1:
Diagram 1.1 shows the structure of an atom.

(a) P and Q are subatomic particles.
  Name P and Q. [2 marks]

(b) What is the charge of P? [1 mark]

(c) What is the nucleon number of this atom? [1 mark]

(d) Diagram 1.2 shows the structure of three atoms.
(i) Which atoms are isotopes? [1 mark]
 Mark (\/) your answers in the box provided in Diagram 1.2.

(ii) Based on Diagram 1.2, complete the sentence below.
Isotopes are atoms of an element which have different number of nucleons but the same number of ______________. [1 mark]

P: Electron
Q: Neutron





4.9.1 Analysing Changes in the States of Matter (Structured Questions)

Question 1:
Diagram below shows the changes in the state of matter of a substance.
Based on the Diagram,
(a) name the processes R, S and T using the following information. [3 marks]

(b) What happens to the kinetic energy of the particles in the substance during process R? [1 mark]

(c) What happens to the movement of the particles in the substance during process S? [1 mark]

(d) Draw the particle arrangement in X in the box provided below. [1 mark]

R: Melting
S: Freezing
T: Condensation

During melting, the kinetic energy of the particles increases.

During freezing, the particles slowing down in their motion and form a pattern, becoming a solid.


6.1 Types of Nutrition

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6.1 Types of Nutrition
Autotrophic Nutrition
1.  An autotroph is an organism that synthesise complex organic molecules from inorganic molecules such as air and water.
2.   Autotrophs are able to synthesise their food by
            (a)  photosynthesis
            (b)  chemosynthesis
3.  Photosynthesis is the process in which green plants and algae, called photoautotrophs, produce organic molecules from carbon dioxide and water using sunlight as a source of energy.
4.  Chemosynthesisis the process in which chemoautotrophs synthesise organic compounds by oxidizing inorganic substances such as hydrogen sulphide and ammonia.

Heterotrophic Nutrition
1.  Heterotrophs are organisms that cannot synthesise their own nutrients but instead must obtain the nutrients from other organisms.
2.  Heterotrophic nutrition is a type of nutrition in which an organism obtains energy through the intake and digestion of complex organic substances into simpler, soluble substances which are then absorbed into their bodies.
3.   Heterotrophs include animals, fungi and some bacteria.
4.   Heterotrophs may practice holozoic nutrition, saprophytism or parasitism

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Holozoic Nutrition
1.   Most animals like humans, herbivores and carnivores are holozoic heterotrophs.
2.   In holozoic nutrition, the organisms feed by ingesting solid organic matter which is subsequently digested and absorbed into their body.

Saprophytic Nutrition (Saprophytism)
1.   In saprophytism, the organisms called saprophytes, feed on dead and decaying organic matter.
2.   Bacteria and fungi are examples of saprophytes.
3.   Saprophytes are sometimes called decomposer.

Parasitic Nutrition (Parasitism)
1.   Parasitism is a close association in which an organism, the parasite, obtains nutrients by living on or in the body of another living organism, the host.
2.   Parasites which live on the body of the host called ectoparasitesFor examples, fleas, ticks and leeches.
3.   Parasites which live in the body of the host called endoparasites. For example, the tapeworms which infest the human intestinal tract.
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