When chromosomes fail to separate

Example of Meiotic Nondisjunction that causes disease like Down Syndrome

How meiosis work?

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http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

Stages of meiosis

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter3/animation__stages_of_meiosis.html
MEIOSIS I
Prophase I
• The chromosomes begin to condense. They become shorter, thicker and clearly visible.
• The homologous chromosomes come together to form bivalent through a process called synapsis.
• Non-sister chromatids exchange segments of DNA in a process known as crossing over.
• Crossing over results in a new combination of genes on a chromosome.
• The points at which segments of chromatids cross over are called chiasmata.
• At the end of prophase I, the nucleolus and nuclear membrane disappear.
• The two pairs of centrioles migrate to the opposite poles of the cells.
• These features are similar to those of prophase during mitosis.
Metaphase I
• The chromosomes are lined up side by side as tetrads on the metaphase plate.
• The chromosomes are still in homologue pairs.
• The centromere does not divide.
Anaphase I
• The spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell.
• Each chromosome still consists of two sister chromatids which move as a single unit.
• Although the cell started with four chromosomes, only two chromosomes (each with two sister chromatids) move towards each pole.
Telophase I
• The chromosomes arrive at the poles.
• Each pole now has a haploid daughter nucleus because it contains only one set of chromosomes.
• The spindle fibres disappear.
• The nuclear membrane reappears to surround each set of chromosomes.
• The nucleolus then reappears in each nucleus.
Cytokinesis
• Cytokinesis usually occurs simultaneously with Telophase I, resulting in two haploid daughter cells, each receiving one chromosome from the homologous pair.
• Meiosis II follows immediately after cytokinesis, usually with no interphase between them.
• DNA replication does not occur and the chromosomes remain in a condensed state.
MEIOSIS II
Prophase II
• The nuclear membranes of the daughter cells disintegrate again.
• The spindle fibres reform in each daughter cell.
Metaphase II
• The chromosomes, each still made up of sister chromatids, are positioned randomly on the metaphase plate with the sister chromatids of each chromosome pointing towards the opposite poles.
• Each sister chromatid is attached to the spindle fibres at the centromere.
Anaphase II
• The centromere of the sister chromatids finally separate, and the sister chromatids of each chromosome are now individual chromosomes.
• The chromosomes move towards the opposite poles of the cell.
Telophase II
• Finally, the nucleolus and nuclear membranes reform. The spindle fibres break down.
• Cytokinesis follows and four haploid daughter cells are formed, each containing half the number of chromosomes and is genetically different from the parent diploid cell.
• These haploid cells (n) will develop into gametes.

Cytokinesis in animal and plant cell

How cancer develops - Uncontrolled cell division

This video demonstrates how cancer growth happens in human body. It is due to uncontrolled cell division.

Cloning Of Dolly, the sheep

Tissue culture

Step 1: Weigh out 2.5 g of nutrient agar and add to 250 ml of distilled water.
Step 2 : Then add hormone into the agar solution. Heat and stir until the agar dissolves.
Step 3 :Pour the hot nutrient agar into several test tubes about 5 cm3 in height.
Allow the agar to cool and solidify in each test tube.
Step 4 :Germinate some mustard seed in a warm lighted place until the cotyledon starts to unfold.
Step 5 : Cut the tips of the seedling just above the shoot apex (meristem).These tissues are called explants.
Step 6 : Put one explant in each test tube.
Step 7 : Cover the tubes with a cling film and place the tubes into a rack by the window.
Step 8 : The tissue cells are left to divide by mitosis to produce a mass of loosely arranged and undifferentiated cells called callus. The callus will then grow into plantlets(little plants) which will grow into adult plants.

Answers to Amali Proses Sains Pg 28-29

Section A

1. a) Draw a graph of percentage of burst red blood cells against concentration of salt solution from Table 1.

b)(i) about 0.435 g/100cm³ (read from graph)

(ii) 0.55 g/100cm³(where the graph intersects the x- axis) No bursting of red blood cells occurs for this concentration because it is isotonic to the concentration of RBC.

c)(i) The RBC will shrink/crinkle.

(ii) At concentration more than 0.55 g/100cm³ , water molecules will diffuse out from the RBC by osmosis. As a result, RBC will shrink due to loss of water.

2. a)(i) Solution X is hypotonic to the cell sap of potato cells. 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 cells 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 length of the strip.

(iii) Solution Z is hypertonic to the cell sap of potato cells. Water molecules out from the vacuoles of the potato cells by osmosis. The cells shrinks and plasmolysis takes place.

(b)(i) Hard

(ii) Soft

(c) The use of excessive fertilizers will increase the osmotic concentration in the soil water, causing water molecules to move out from the root hairs. The plant will wilt and 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 without the use of energy.

Facilitated diffusion

Movement of big molecules along a concentration gradient with the help of protein carriers across the plasma membrane and also without the use of energy.

Osmosis

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

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.

b)

Active transport	Osmosis
Active transport needs energy	Osmosis does not need energy
Active transport involves the movements of molecules or ions against a concentration gradient.	Osmosis transport involves the movements of water molecules along a concentration gradient.
Active transport takes places through the plasma membrane of a living cell.	Osmosis takes places through a semi-permeable membrane.
Active transport needs protein carriers	Osmosis does not need protein carriers

4.(a)

Plasma membrane is selectively permeable. It 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.

(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 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.

(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.

Answers to Amali Proses Sains Pg 20-22

Aim :To study the effects of hypotonic, hypertonic and isotonic solutions to a plant cell

Discussion:

1a) 0.5 M sucrose solution

b) 0.2 M sucrose solution

c) 0.8 M sucrose solution

2. Plasmolysis

3. 0.8 M sucrose solution is hypertonic to the cell sap of onion cell. Water molecules moves out of the vacuole by osmosis causing the vacuole to shrink. The plasma membrane detaches from the cell wall. The cell becomes flaccid.

4. 0.2 M sucrose solution is hypotonic to the cell sap of onion cell. Water molecules moves into the vacuole by osmosis causing the vacuole to expand outwards and press both the vacuole and the cell wall. The cell becomes turgid.

5. The cell becomes turgid again due to deplasmolysis.

Conclusion

Epidermal cell of onion becomes turgid when immersed in a hypotonic solution. In 0.5M sucrose solution, which is isotonic, there is no change in shape and condition of the cell. In a hypertonic solution, the cell becomes flaccid due to loss of water from the vacuole of the cell.

Answers to Amali Proses Sains Pg 18-19

Aim : To study the effects of hypotonic, hypertonic and isotonic solutions to animal cells

Discussion:

1a) 0.17 M sodium chloride solution

b) Distilled water

c) 0.51M sodium chloride solution

2. Haemolysis

3. Distilled water is hypotonic to the protoplasm of the red blood cells. Water molecules move into the cytoplasm of the red blood cells by osmosis causing the cells to swell and burst. This is known as haemolysis.

4. 0.51M sodium chloride solution is hypertonic to the protoplasm of the red blood cells. Water molecules move out from the cytoplasm of the red blood cells by osmosis causing the cells to shrink. This is known as crenation.

Conclusion

Red blood cells in hypotonic solution will swell and burst. This phenomenon is known as haemolysis. In hypertonic solution, the red blood cells will shrink and is known as crenation. There is no change in shape and size of red blood cells in an isotonic solution.

Answers to Amali Proses Sains Pg 15-17

Aim : To study the movement of substances across a semi permeable membrane.

Hypothesis: Molecules which are smaller than the pores of the Visking tubing are able to move across the plasma membrane

MV : Size of solute molecules

RV : Colour of Iodine/Benedict  solution

FV : Temperature/time

Solution in	Content	Iodine test		Benedict test
		Initial	Final
Visking tubing	Glucose solution + starch suspension	Colourless	Dark blue	Red precipitate
Beaker	Distilled water + iodine solution	Yellow	Light yellow	Red precipitate

Discussion

1.       Iodine molecules are smaller than the starch molecules. Thus the iodine molecules are able to move into the visking tubing while the starch molecules cannot move out from the visking tubing.

2.       Glucose molecules are smaller than the starch molecules.

3.       Starch needs to be hydrolysed to glucose in the alimentary canal so that the glucose molecules are small enough to diffuse into the epithelium cells of the villi and into the blood capillaries.

Conclusion

Yes, the hypothesis is accepted. Molecules which are smaller than the pores of the Visking tubing are able to move across the plasma membrane.