HANDS ON CHAPTER 3

Mastery Exercise

Objective Questions

1. D 2. B 3. D 4. C 5. C

6. C 7. C 8. A 9. C 10. D

11. C 12. B 13. C 14. B 15. C

Subjective Questions 

Section A

1. (a) Plot your own graph scale for y axis ----100 80 60 40 20… scale for x axis 0 0.30 0.35 0.40 0.45 0.50 0.55 Concentration of salt solution (g/100 cm3) (b) (i) 0.435 g/100 cm3 (ii) 0.55 g/100 cm3. No bursting of red blood cells occurs in this concentration because it is isotonic to the concentration of red blood cells. (c) (i) The red blood cells will shrink.  (ii) At concentration of more than 0.55 g/100 cm3, water molecules will move out from the red blood cells by osmosis to its surrounding. As a result, red blood cells will shrink due to loss of water.  2. (a) (i) Solution X is hypotonic to the cell sap of potato cell. Water molecules from solution X move into the vacuoles of the potato cells by osmosis. The enlarged vacuole will push against the cytoplasm, causing the cell to inflate. This causes the potato strip to lengthen. (ii) Solution Y is isotonic to the cell sap of potato cells. The rate of movement of water molecules in and out of the cells is the same. Therefore, there is no change in the length of the strip. (iii) Solution Z is hypertonic to the cell sap of potato cells. Water molecules move out from the vacuole of the cells. Plasmolysis takes place and the potato strip shrinks. (b) (i) Hard (ii) Soft (c) The use of excessive fertiliser will increase the osmotic concentration in the soil water, causing water molecules to move out from the root hair. The plant will wilt and may die. 

Section B

3. (a) Simple diffusion – Movement of molecules in gas or liquid from a region of high concentration to a region of lower concentration.

Facilitated diffusion – Movement of big molecules along a concentration gradient with the help of protein carriers across the plasma membrane.

Resapan berbantu – Pergerakan molekul besar merentas membran plasma mengikut kecerunan kepekatan dengan bantuan protein pembawa.

Osmosis – Movement of water molecules from a region of less concentrated solution to a region of more concentrated solution across a semi-permeable membrane.

Osmosis – Pergerakan molekul air merentas membran separa telap dari kawasan berkepekatan rendah ke kawasan berkepekatan tinggi.

Active transport – Movement of particles across the plasma membrane against the concentration gradient with the help of protein carriers and the presence of energy from ATP.

Active transport	Osmosis
(1) Needs energy.	(1)Does not need energy.
(2) Movements of molecules or ions   against a concentration gradient.	(2) Movement of water        molecules along a concentration gradient.

4. (a) • Plasma membrane is selectively permeable.

• Permits lipid-soluble molecules such as glycerol, vitamins A, D, E and K to move across.

• Small, uncharged molecules such as water move freely across.

• Large molecules such as glucose and amino acids move across the plasma membrane with the aid of carrier proteins.

• Larger molecules such as starch cannot move across the plasma membrane. 

Maximum 4

(b) • Plasma membrane consists of phospholipids bilayer and proteins.

• Phospholipid molecule consists of a polar head which is hydrophilic and a pair of non-polar fatty acid tails which is hydrophobic.

• Two types of proteins which are pore proteins and transport proteins.

• Plasma membrane is semi-permeable which allows certain substances to move in and out freely.

• Small, uncharged molecules such as oxygen and carbon dioxide move freely through the phospholipids bilayer through simple diffusion. 

• Water molecules which are attracted to the hydrophilic heads of the phospholipids move across through osmosis.

• Lipid-soluble molecules such as fatty acids and ethanol dissolve in the lipid bilayer and move across through simple diffusion.

• Large, water-soluble molecules such as glucose and amino acids require the aid of transport proteins to move them across the plasma membrane through facilitated diffusion or active transport.

• Ions such as K+ and Na+ are transported across the plasma membrane through facilitated diffusion or active transport with the help of transport proteins.

Maximum / Maksimum 10

(c) • Vegetables soak in salt solution which is hypertonic to the cell sap of vegetable cells.

• Harmful insecticides or fungicides which had been sprayed on the vegetables earlier diffuse out of the cells to the salt solution.

• Water from the cell sap in the vacuole also diffuses out the salt solution through osmosis.

• The vegetables become flaccid.

• This action cleans the vegetables of harmful insecticides but causes the vegetables to be flaccid and soft.

Maximum / Maksimum 6

Written Practical

1. (a) (i) The length of potato core in 0.1 M sucrose solution increases. The length of potato core in 0.4 M sucrose solution decreases.

(ii) 0.1 M sucrose solution is hypotonic to the cell sap of the potato cells. 0.4 M sucrose solution is hypertonic to the cell sap of potato cells.

(b) The concentration of a solution is isotonic to the cell sap of a potato cell if the solution does not change the length of the potato core.

(c) (i) & (ii)

Initial (cm)	Final (cm)	Change in length of the potato core (cm)
Mean / Min	Mean / Min
5.0	5.25	+ 0.25
5.0	5.10	+ 0.10
5.0	4.90	– 0.10
5.0	4.70	– 0.30

(d) (i) Concentration of the sucrose solution

(ii) Length of the potato core

(iii) Temperature

(e) (i) Use different concentration of sucrose solution

(ii) Measure and record length of potato cores using a ruler

(iii) Keep surrounding temperature constant

(f) plot your own graph

0.1 0.3 0.2 0.1 –0.1 –0.2 –0.30 0.2 0.3 0.4 0.5 Concentration of the sucrose solution (M)  Change in length of the potato core (cm)

(g) 0.24 M. There is no change in the length of the potato core at this concentration. This means the rate of movement of water molecules in and out of the potato cells is the same.

(h) (i) Osmosis

(ii) The cell sap is hypertonic to the 0.2 M sucrose solution. Water molecules from the sucrose solution move into the vacuoles of the potato cells, causing the vacuoles to exert pressures on the cytoplasm. The cells swell and lengthens the potato core. 

2. Aim: To study the effects of isotonic, hypotonic and hypertonic solutions on animal cell.

Problem Statement: What is the effect of isotonic, hypotonic and hypertonic solutions on an animal cell?

Hypothesis: An animal cell will swell and may burst when put into a hypotonic solution. An animal cell will shrink when put into a hypertonic solution. There is no change in the size and shape of the animal cell when put into an isotonic solution.

Variables / Pemboleh ubah:

Manipulated: Concentration of solutions

Responding: Conditions of cells

Fixed: Time, temperature, type of cells

Materials: Chicken blood (sodium citrate added to prevent it from clotting), 0.17 M sodium chloride solution, 0.50 M sodium chloride solution and distilled water.

Apparatus: Slides, cover slips and light microscope

Procedur :

1. Label four slides as A, B, C and D.

2. Put a drop of blood on slide A and cover with a cover slip. Observe under a light microscope.
3. Put a drop of distilled water on slide B and cover with a cover slip. Put a drop of blood at the edge of the cover slip.

4. Observe the slide under a microscope when the blood is drawn into the water.

5. Repeat steps 3 and 4 by using 0.17 M and 0.50 M sodium chloride solutions on slides C and D respectively.

Conclusion: Red blood cells swell and burst into fragments of cytoplasm when put into hypotonic solution. In hypertonic solution, red blood cells shrink due to water loss. There is no change in the cells when immersed in isotonic solution. Hypothesis is accepted.

Note from teacher!

Please study the pictures of cross section of plant, skin and intestine. You can go thru the pictures from the internet or textbook. Good luck to all for the exam!


-Pn. Ziakiah Omar

Best of luck! (:

Good luck to all science students who's taking Biology exam  tomorrow! (:

NOTES: Cross section of leaf

Leaf Structure:
A leaf is made of many layers that are sandwiched between two layers of tough skin cells (called the epidermis). The epidermis also secretes a waxy substance called the cuticle. These layers protect the leaf from insects, bacteria, and other pests. Among the epidermal cells are pairs of sausage-shaped guard cells. Each pair of guard cells forms a pore (called stoma; the plural is stomata). Gases enter and exit the leaf through the stomata.

Most food production takes place in elongated cells called palisade mesophyll. Gas exchange occurs in the air spaces between the oddly-shaped cells of the spongy mesophyll.

Veins support the leaf and are filled with vessels that transport food, water, and minerals to the plant.

Cross section of skin: organ that forms the outer covering of a human body.
Pores: minute holes from which sweat and sebum are secreted.
Hair shaft: a filament that grows from the skin.
Epidermis: outer layer of the skin.
Dermins or true skin: middle layer of the skin.
Sebaceous gland: gland that secretes sebum, which lubricates the skin and hair.
Subcutaneous tissue: deep subcutaneous layer.
Connective tissue: tissue that consists of cells and fibres and which connects and supports.
Matrix: cells that allow hair growth copyright bernard dery infovisual.
Nerve ending: part of the skin that senses stimuli.
Adipose tissue (fat): fat-producing cells.
Arteriole: network of blood vessels that carries blood from the heart to the organs.
Venule: network of blood vessels that carries blood from the organs to the heart.
Sweat gland: gland that produces and secretes sweat.
Pilo erectile muscle: muscle that elevates the hair.
Capillaries: blood vessels that allow the exchange of various nutriments and wastes among cells.
Sweat pore: minute hole that secretes perspiration.
Skin surface: top of the epidermis.

Structure and function

The structure and function can be described both as gross anatomy and at a microscopic level. The intestinal tract can be broadly divided into two different parts, the small and large intestine.^[2] People will have different sized intestines according to their size and age.

The lumen is the cavity where digested food passes through and from where nutrients are absorbed. Both intestines share a general structure with the whole gut, and are composed of several layers. Going from inside the lumen radially outwards, one passes the mucosa (glandular epithelium and muscularis mucosa), submucosa, muscularis externa (made up of inner circular and outer longitudinal), and lastly serosa.

§  Along the whole length of the gut in the glandular epithelium are goblet cells. These secretemucus which lubricates the passage of food along and protects it from digestive enzymes. In the small intestine, villi are vaginations (folds) of the mucosa and increase the overall surface area of the intestine while also containing a lacteal, which is connected to the lymph system and aids in the removal of lipids and tissue fluid from the blood supply. Microvilli are present on the epithelium of a villus and further increase the surface area over which absorption can take place. Pocket-like invaginations into the underlying tissue are termed Crypts of Lieberkühn. In the large intestines, villi are absent and a flat surface with thousands of crypts is observed.

§  Underlying the epithelium is the lamina propria, which contains myofibroblasts, blood vessels, nerves, and several different immune cells.

§  The next layer is the muscularis mucosa which is a layer of smooth muscle that aids in the action of continued peristalsis and catastalsisalong the gut. The submucosa contains nerves (e.g. Meissner's plexus), blood vessels and elastic fibre with collagen that stretches with increased capacity but maintains the shape of the intestine.

§  Surrounding this is the muscularis externa which comprises longitudinal and circular smooth muscle that again helps with continued peristalsis and the movement of digested material out of and along the gut. In between the two layers of muscle lies Auerbach's plexus.

§  Lastly there is the serosa which is made up of loose connective tissue and coated in mucus so as to prevent friction damage from the intestine rubbing against other tissue. Holding all this in place are the mesenteries which suspend the intestine in the abdominal cavity and stop it being disturbed when a person is physically active.

The large intestine hosts several kinds of bacteria that deal with molecules the human body is not able to break down itself.^{[citation needed]} This is an example of symbiosis. These bacteria also account for the production of gases inside our intestine (this gas is released as flatulence when eliminated through the anus). However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the hypothalamus) and the reabsorption of sodium, as well as any nutrients that may have escaped primary digestion in the ileum.