Dear Marists,
Please complete all the topical TYS Qns for the topics that will be tested for prelim 1.
You may find on the right side column links to the TYS answers.
Also you will be given 2011 and 2012 MSHS prelim 1 papers for practice and revision.
Topics to be tested for prelim 1 include after Topic 5 (Nutrition in man) till Topic 15.2 (Repro in man).
Please begin your revision asap if you have yet to start.
Nutrition and Transport in Man-Main Points
TRANSPORT IN MAN (T6.1, 6.2 ONLY)
-Structure of arteries: thick muscular and elastic walls / no valves
-Structure of veins: thin muscular walls / valves present / movement of blood aided by contraction of skeletal muscles on the veins (blood is pushed along the vein)
-Structure of capillaries: one cell thick endothelium / thin walled (increase rate of exchange) of materials by diffusion
-Cardiac cycle: atrial systole / diastole / ventricular systole / diastole / contraction / relaxation / cardiac muscle / bicuspid valve / tricuspid valve / blood flows / pulmonary artery / aorta / semi lunar valves (aortic and pulmonary valve)
NUTRITION IN MAN
main parts of the digestive system (name and know the functions)
-Digestion take place in 3 places:
a)Mouth: Starch / salivary amylase
b)Stomach: pepsin / protein to polypeptides / HCl / functions of HCl
c)Small intestine: alkaline / villus / pancreas / pancreatic juice(TAL) / intestinal juice(EELMLS) / No digestion in the large intestine
-2 types of amylase: salivary, pancreatic (be specific)
-know products of all the enzyme reactions in the digestive system
eg: starch => maltose
fats => fatty acids + glycerol
proteins => peptones/polypeptides => amino acids
-assimilation IS NOT digestion or absorption!!!
Function of hepatic portal vein (from small intestine to liver for assimilation)
-Absorption: small intestine / villus / adaptations of villus/ lacteals / fatty acids / glycerol
-Assimilation: liver / bile / glycogen / excess glucose / deamination of excess amino acids / urea / urea excreted in urine
-Other functions of liver NOT related to digestive system: breakdown red blood cells / breakdown alcohol
-Structure of arteries: thick muscular and elastic walls / no valves
-Structure of veins: thin muscular walls / valves present / movement of blood aided by contraction of skeletal muscles on the veins (blood is pushed along the vein)
-Structure of capillaries: one cell thick endothelium / thin walled (increase rate of exchange) of materials by diffusion
-Cardiac cycle: atrial systole / diastole / ventricular systole / diastole / contraction / relaxation / cardiac muscle / bicuspid valve / tricuspid valve / blood flows / pulmonary artery / aorta / semi lunar valves (aortic and pulmonary valve)
NUTRITION IN MAN
main parts of the digestive system (name and know the functions)
-Digestion take place in 3 places:
a)Mouth: Starch / salivary amylase
b)Stomach: pepsin / protein to polypeptides / HCl / functions of HCl
c)Small intestine: alkaline / villus / pancreas / pancreatic juice(TAL) / intestinal juice(EELMLS) / No digestion in the large intestine
-2 types of amylase: salivary, pancreatic (be specific)
-know products of all the enzyme reactions in the digestive system
eg: starch => maltose
fats => fatty acids + glycerol
proteins => peptones/polypeptides => amino acids
-assimilation IS NOT digestion or absorption!!!
Function of hepatic portal vein (from small intestine to liver for assimilation)
-Absorption: small intestine / villus / adaptations of villus/ lacteals / fatty acids / glycerol
-Assimilation: liver / bile / glycogen / excess glucose / deamination of excess amino acids / urea / urea excreted in urine
-Other functions of liver NOT related to digestive system: breakdown red blood cells / breakdown alcohol
Nutrition in Man- Summary
Nutrition in mammals involves:
1. Ingestion of food into body
2. Digestion of food into smaller molecules that can be absorbed into cells
3. Absorption and uptake of nutrients into cells
4. Assimilation: Use of nutrients for energy or making protoplasm
5. Egestion: Removal of undigested and unabsorbed material from the body
This involves the action of the digestive system, which consists of the gut (tube stretching from mouth to anus) and the other glands such as the liver and pancreas.
Gut structure:
Muscle layer: 2 layers of muscle (stomach has 3 layers) arranged in rings (circular muscle), and lengthwise (longitudinal muscle). These contract and relax to bring about peristalsis to push food along the gut.
Digestion
Can be classified as:
1. Physical: Mechanical breakdown of food into smaller particles, without the use of enzymes. Eg. Mastication in buccal cavity, churning in stomach, emulsification of fats in small intestine.
2. Chemical: Breakdown of food, involving the breaking of chemical bonds, which hence requires the action of enzymes. Eg. Digestion/Hydrolysis of amylase into maltose by amylase.
Important note: When describing chemical digestion processes, you must include in your answer:
1. Name of enzyme
2. Source of enzyme (where is enzyme made?)
3. Substrate that enzyme acts on
4. Product formed from reaction
Additional Notes
1. All proteases (enzymes that act on proteins/peptones) usually end with "-in" (pepsin, rennin, trypsin, erepsin).
2. Proteases that act on proteins must be produced in the inactive form inside cells, or the protease will cause the destruction of the cell as it will digest the proteins in the cell. Activation of the proteases depends on the type of protease: Those in the stomach are activated by acid, those in the small intestine (trypsin) is activated by another enzyme, enterokinase (from intestinal glands). This ensures protease is only activated in the lumen of the gut.
3. Bile salts allow for PHYSICAL digestion (emulsification) of fats into smaller fat globules, which increases the surface area available for lipase to act on, hence increasing rate of lipase action. Bile salts also allow for the absorption of fatty acids into epithelial cells of villus. They allow the entry of fatty acids and glycerol, after which they then return to the lumen of the small intestine, where the process is repeated again.
4. Bile pigments DO NOT play a digestive function. They are just excretory products, formed from the breakdown of haemoglobin during the destruction of old red blood cells. Of course, since they are pigments, they give faeces their brown colour (but that's not a function!), and are removed out along with the faeces.
5. Digestion of fats: Fats are physically broken into fat globules (emulsification) by action of bile (produced by liver, stored in gall bladder). This increases surface area for lipase (from pancreas and intestinal glands) to digest the lipids into fatty acids and glycerol (chemical digestion).
1. Ingestion of food into body
2. Digestion of food into smaller molecules that can be absorbed into cells
3. Absorption and uptake of nutrients into cells
4. Assimilation: Use of nutrients for energy or making protoplasm
5. Egestion: Removal of undigested and unabsorbed material from the body
This involves the action of the digestive system, which consists of the gut (tube stretching from mouth to anus) and the other glands such as the liver and pancreas.
Gut structure:
Muscle layer: 2 layers of muscle (stomach has 3 layers) arranged in rings (circular muscle), and lengthwise (longitudinal muscle). These contract and relax to bring about peristalsis to push food along the gut.
Digestion
Can be classified as:
1. Physical: Mechanical breakdown of food into smaller particles, without the use of enzymes. Eg. Mastication in buccal cavity, churning in stomach, emulsification of fats in small intestine.
2. Chemical: Breakdown of food, involving the breaking of chemical bonds, which hence requires the action of enzymes. Eg. Digestion/Hydrolysis of amylase into maltose by amylase.
Important note: When describing chemical digestion processes, you must include in your answer:
1. Name of enzyme
2. Source of enzyme (where is enzyme made?)
3. Substrate that enzyme acts on
4. Product formed from reaction
Additional Notes
1. All proteases (enzymes that act on proteins/peptones) usually end with "-in" (pepsin, rennin, trypsin, erepsin).
2. Proteases that act on proteins must be produced in the inactive form inside cells, or the protease will cause the destruction of the cell as it will digest the proteins in the cell. Activation of the proteases depends on the type of protease: Those in the stomach are activated by acid, those in the small intestine (trypsin) is activated by another enzyme, enterokinase (from intestinal glands). This ensures protease is only activated in the lumen of the gut.
3. Bile salts allow for PHYSICAL digestion (emulsification) of fats into smaller fat globules, which increases the surface area available for lipase to act on, hence increasing rate of lipase action. Bile salts also allow for the absorption of fatty acids into epithelial cells of villus. They allow the entry of fatty acids and glycerol, after which they then return to the lumen of the small intestine, where the process is repeated again.
4. Bile pigments DO NOT play a digestive function. They are just excretory products, formed from the breakdown of haemoglobin during the destruction of old red blood cells. Of course, since they are pigments, they give faeces their brown colour (but that's not a function!), and are removed out along with the faeces.
5. Digestion of fats: Fats are physically broken into fat globules (emulsification) by action of bile (produced by liver, stored in gall bladder). This increases surface area for lipase (from pancreas and intestinal glands) to digest the lipids into fatty acids and glycerol (chemical digestion).
Transport in Plants- Practice Questions
The graph above shows the water uptake and water loss by a plant over a period of 24 hours.
(a) Describe the relationship between water uptake and water loss. [1]
(b) Name the process through which water is lost to the atmosphere. [1]
(c) Between which hours does water loss exceed water uptake? [1]
(d) Between which hours does the plant have the highest water uptake and water loss? [1]
(e) Suggest a reason why the highest water loss occurs at this time. [1]
(f) State what would happen to the plant if water loss continues to exceed water uptake. [1]
ANSWERS
(a) As water loss increases, water uptake also increases ; / as water loss decreases, water uptake also decreases ;
(b) Transpiration ;
(c) 6.30 am to 8.00 pm ;
(d) Around 3.00 pm to 4.00 pm ;
(e) Due to high temperature which increases rate of diffusion and hence rate of transpiration ;
(f) Cells in plant lose turgor/ become flaccid, leaves will start to droop, wilting occurs ;
Nutrition in Plants- Practice Questions
1. The figure below shows an apparatus used for water culture experiments.Several plants are grown like this, in identical conditions. Some, the controls, are given a culture solution containing all the minerals needed by plants. Others have a solution from which one mineral is missing. By comparing with the control plants, the effects of a lack of each mineral can be seen.
(a) Explain why the glass vessel is blackened. [3]
(b) Explain the need for the glass tubing. [2]
(c) If the element nitrogen is absent from the culture solution. How will this affect the plant and why? [2]
ANSWERS
1(a) To reduce amount of sunlight entering to prevent algal growth;
Which may grow around the roots and hinder the plant’s growth;
By competing for nutrients with the roots / blocking and reducing surface area of roots that can take up minerals;
(b) Glass tube to supply oxygen; which the roots need for respiration;
(c) Absence of nitrogen (in nitrates) cause poor growth/fewer leaves/small and pale green leaves leading to death;
As nitrogen is essential for amino acid and protein synthesis;
[Reminder: Plants use nitrates for a nitrogen source, not nitrogen gas!]
2.The figure below shows a picture of a leaf attached to a plant throughout the experiment.
6 discs were cut out from regions X, Y and Z of the leaf at 10 a.m., 4 p.m. and 10 p.m.. The plant may have received some treatment before the discs were cut and likewise the discs too, before their total dry weight is measured. The steps are show below:
Time / Treatment to plant before removing leaf discs/ Treatment of leaf discs/ Dry weight of leaf discs (mg)
10 a.m./ exposed to sunlight/ killed in steam/ 186
4 p.m./ exposed to sunlight/ none/ 209
10 p.m./ kept in the dark for 6 hours/ none/ 198
(a)(i) What is the biological process that causes the change in dry weight of the leaf discs between 10 a.m. and 4 p.m.? Support your answer with reasons. [2]
(ii) What is the biological process that causes the change in dry weight of the leaf discs between 4 p.m. and 10 p.m.? Support your answer with reasons. [2]
(b) Why is dry weight measured instead of fresh weight? [2]
ANSWERS
2(a)(i) Photosynthesis [0.5]
Dry weight increases from 186 to 209 mg, as the leaf discs cut at 4 pm were exposed to sunlight for 6 hrs more than those cut at 10 am [0.5]
Cells in the dics cut at 4 pm would have carried out photosynthesis for a longer period, and would have produced more glucose which would be stored as starch, leading to an increase in dry weight;
(a)(ii) Respiration [0.5]
Stored starch is being converted to glucose for respiration as photosynthesis has stopped in the absence of light/rate of respiration exceeds rate of photosynthesis;
Breakdown of starch and glucose would lead to a decrease in weight from 209 to 198 mg [0.5]
(b) Dry weight is more accurate because it is not affected by the water content of the leaf discs;
Water content is easily affected by different environmental conditions/amount of water absorbed by the plant;
(a) Explain why the glass vessel is blackened. [3]
(b) Explain the need for the glass tubing. [2]
(c) If the element nitrogen is absent from the culture solution. How will this affect the plant and why? [2]
ANSWERS
1(a) To reduce amount of sunlight entering to prevent algal growth;
Which may grow around the roots and hinder the plant’s growth;
By competing for nutrients with the roots / blocking and reducing surface area of roots that can take up minerals;
(b) Glass tube to supply oxygen; which the roots need for respiration;
(c) Absence of nitrogen (in nitrates) cause poor growth/fewer leaves/small and pale green leaves leading to death;
As nitrogen is essential for amino acid and protein synthesis;
[Reminder: Plants use nitrates for a nitrogen source, not nitrogen gas!]
2.The figure below shows a picture of a leaf attached to a plant throughout the experiment.
6 discs were cut out from regions X, Y and Z of the leaf at 10 a.m., 4 p.m. and 10 p.m.. The plant may have received some treatment before the discs were cut and likewise the discs too, before their total dry weight is measured. The steps are show below:
Time / Treatment to plant before removing leaf discs/ Treatment of leaf discs/ Dry weight of leaf discs (mg)
10 a.m./ exposed to sunlight/ killed in steam/ 186
4 p.m./ exposed to sunlight/ none/ 209
10 p.m./ kept in the dark for 6 hours/ none/ 198
(a)(i) What is the biological process that causes the change in dry weight of the leaf discs between 10 a.m. and 4 p.m.? Support your answer with reasons. [2]
(ii) What is the biological process that causes the change in dry weight of the leaf discs between 4 p.m. and 10 p.m.? Support your answer with reasons. [2]
(b) Why is dry weight measured instead of fresh weight? [2]
ANSWERS
2(a)(i) Photosynthesis [0.5]
Dry weight increases from 186 to 209 mg, as the leaf discs cut at 4 pm were exposed to sunlight for 6 hrs more than those cut at 10 am [0.5]
Cells in the dics cut at 4 pm would have carried out photosynthesis for a longer period, and would have produced more glucose which would be stored as starch, leading to an increase in dry weight;
(a)(ii) Respiration [0.5]
Stored starch is being converted to glucose for respiration as photosynthesis has stopped in the absence of light/rate of respiration exceeds rate of photosynthesis;
Breakdown of starch and glucose would lead to a decrease in weight from 209 to 198 mg [0.5]
(b) Dry weight is more accurate because it is not affected by the water content of the leaf discs;
Water content is easily affected by different environmental conditions/amount of water absorbed by the plant;
Nutrition in Plants- A Summary
What is photosynthesis?
It is the process by which green plants trap light energy using chlorophyll and convert it to chemical energy for the production of glucose from water and carbon dioxide.
Oxygen is released as a by-product.
Adaptations of the leaf
Leaf is an organ specialized for photosynthesis.
Its broad and thin lamina provides and large surface area for maximum absorption of light.
The thin lamina allows carbon dioxide to enter/diffuse into the cells quickly.
The palisade cells contains numerous chloroplast and are packed closely together at the upper surface of the leaf.
This enables them to absorb light energy efficiently.
The spongy mesophyll cells are loosely packed so that large intercellular spaces are present for rapid diffusion of gaseous exchange.
The numerous stomata at the lower epidermis allows rapid gaseous exchange between the leaf and the air.
The extensive vain system of xylem and phloem help to provide rapid transport of water to, and manufactured food from the leaf.
Effects of varying light intensity on photosynthesis.
Light energy is trapped by chlorophyll to split water molecules during photosynthesis.
Increasing light energy will speed up photolysis, hence increasing photosythesis.
Effects of varying wavelights on photosynthesis.
Red and blue wavelights highly absorbed.
Green and yellow reflected.
More light absorbed will increase rate of photosynthesis.
Effects of varying carbon dioxide on photosynthesis
Increased CO2, increases rate of glucose produced, resulting in increase in rate of photosynthesis.
Effects of varying temperature on photosynthesis
Temperature affects rate of enzyme-catalysed reaction in photosynthesis.
Low temperature: enzymes inactive
High temperature: enzymes denature and no photosynthesis takes place.
MCQ Questions
1. The word equation which best describes photosynthesis is .
a. carbon dioxide + energy → glucose + oxygen + water
b. glucose + oxygen → water + carbon dioxide + energy
c. glucose + oxygen → water + carbon dioxide + energy
d. water + carbon dioxide + energy → glucose + oxygen
2. Which of the following cells of a leaf do not have chloroplasts?
a. Guard cells
b. Palisade mesophyll
c. Spongy mesophyll
d. Upper epidermis
3. How does most of the carbon dioxide enter the photosynthesising cells of a leaf?
a. Diffusion through the epidermis of the leaf
b. Diffusion through the stomata of the leaf
c. Diffusion through the xylem in the leaf
d. Diffusion through the phloem in the leaf
4. Which of the following statements is the most accurate?
a. Food can travel up the stem in the phloem.
b. Food can travel up or down the stem in the xylem.
c. Food can travel up or down the stem in the phloem.
d. Food can travel down the stem in the phloem.
5. Which of the following conditions is least likely to increase the rate of transpiration in a plant?
a. a rise in temperature.
b. an increase in humidity.
c. increased air movement.
d. increased sunlight
MCQ Answers
1. d
2. d
3. b
4. b
5. b
Structured Question Worked Solutions
1. The equation for photosynthesis is usually given as:
a. Which cell organelle does photosynthesis occur in?
b. Comment on the accuracy of the given equation in describing the process of
photosynthesis.
Solution
a. Chloroplast
b. The equation is not very accurate because it does not show that photosynthesis is a two-step process
only one step is light-dependent and the other is light-independent water is formed during the light-independent stage.
2. Discuss the major adaptations of the leaf to photosynthesis.
Solution
The petiole holds the leaf lamina away from the stem so that the lamina can absorb suffi cient sunlight and air.
The leaf lamina has a large fl at surface compared to its volume.
This enables the leaf to absorb the maximum amount of sunlight for photosynthesis.
A thin expanded lamina ensures that carbon dioxide, the raw material for photosynthesis, can rapidly reach the inner cells of the leaf.
A network of veins extends throughout the leaf. Veins are made of the vascular tissues, xylem and phloem. Xylem transports water and mineral salts to the leaf cells. Phloem transports sugars away from the leaf cells to other parts of the plant. This maintains a concentration gradient so that the photosynthetic reactions proceed in the forward direction.
A waxy cuticle on the leaf epidermis protects the leaf by reducing evaporation of water. Water is an essential raw material for photosynthesis. Lack of water would also make the leaf wilt, reducing surface area for light absorption.
Stomata on the lower epidermis open in sunlight, allowing carbon dioxide to diffuse in and oxygen to diffuse out.
Mesophyll cells of the leaf contain numerous chloroplasts. Chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis.
Mesophyll cells in the upper regions of the leaf (palisade mesophyll) contain more chloroplasts since more light energy can be absorbed near the leaf surface.
An interconnecting system of air spaces in the lower regions of the leaf (spongy mesophyll) allow rapid diffusion of carbon dioxide into mesophyll cells.
3. Discuss why the following statement is true: “Temperature will only increase the rate of photosynthesis to a certain extent. At very high temperatures, the rate of photosynthesis will decrease.”
Solution
Photosynthesis is an enzyme-catalysed reaction.
There will be increased collision of enzyme and substrate as temperature increases.
This results in more enzyme-substrate complex being formed and thus a greater rate of reaction. However, at very high temperatures, enzymes being protein in nature, will be denatured.
The substrate no longer fits into the active site and an enzyme-substrate complex cannot be formed.
Thus the rate of photosynthesis will decrease.
It is the process by which green plants trap light energy using chlorophyll and convert it to chemical energy for the production of glucose from water and carbon dioxide.
Oxygen is released as a by-product.
Adaptations of the leaf
Leaf is an organ specialized for photosynthesis.
Its broad and thin lamina provides and large surface area for maximum absorption of light.
The thin lamina allows carbon dioxide to enter/diffuse into the cells quickly.
The palisade cells contains numerous chloroplast and are packed closely together at the upper surface of the leaf.
This enables them to absorb light energy efficiently.
The spongy mesophyll cells are loosely packed so that large intercellular spaces are present for rapid diffusion of gaseous exchange.
The numerous stomata at the lower epidermis allows rapid gaseous exchange between the leaf and the air.
The extensive vain system of xylem and phloem help to provide rapid transport of water to, and manufactured food from the leaf.
Effects of varying light intensity on photosynthesis.
Light energy is trapped by chlorophyll to split water molecules during photosynthesis.
Increasing light energy will speed up photolysis, hence increasing photosythesis.
Effects of varying wavelights on photosynthesis.
Red and blue wavelights highly absorbed.
Green and yellow reflected.
More light absorbed will increase rate of photosynthesis.
Effects of varying carbon dioxide on photosynthesis
Increased CO2, increases rate of glucose produced, resulting in increase in rate of photosynthesis.
Effects of varying temperature on photosynthesis
Temperature affects rate of enzyme-catalysed reaction in photosynthesis.
Low temperature: enzymes inactive
High temperature: enzymes denature and no photosynthesis takes place.
MCQ Questions
1. The word equation which best describes photosynthesis is .
a. carbon dioxide + energy → glucose + oxygen + water
b. glucose + oxygen → water + carbon dioxide + energy
c. glucose + oxygen → water + carbon dioxide + energy
d. water + carbon dioxide + energy → glucose + oxygen
2. Which of the following cells of a leaf do not have chloroplasts?
a. Guard cells
b. Palisade mesophyll
c. Spongy mesophyll
d. Upper epidermis
3. How does most of the carbon dioxide enter the photosynthesising cells of a leaf?
a. Diffusion through the epidermis of the leaf
b. Diffusion through the stomata of the leaf
c. Diffusion through the xylem in the leaf
d. Diffusion through the phloem in the leaf
4. Which of the following statements is the most accurate?
a. Food can travel up the stem in the phloem.
b. Food can travel up or down the stem in the xylem.
c. Food can travel up or down the stem in the phloem.
d. Food can travel down the stem in the phloem.
5. Which of the following conditions is least likely to increase the rate of transpiration in a plant?
a. a rise in temperature.
b. an increase in humidity.
c. increased air movement.
d. increased sunlight
MCQ Answers
1. d
2. d
3. b
4. b
5. b
Structured Question Worked Solutions
1. The equation for photosynthesis is usually given as:
a. Which cell organelle does photosynthesis occur in?
b. Comment on the accuracy of the given equation in describing the process of
photosynthesis.
Solution
a. Chloroplast
b. The equation is not very accurate because it does not show that photosynthesis is a two-step process
only one step is light-dependent and the other is light-independent water is formed during the light-independent stage.
2. Discuss the major adaptations of the leaf to photosynthesis.
Solution
The petiole holds the leaf lamina away from the stem so that the lamina can absorb suffi cient sunlight and air.
The leaf lamina has a large fl at surface compared to its volume.
This enables the leaf to absorb the maximum amount of sunlight for photosynthesis.
A thin expanded lamina ensures that carbon dioxide, the raw material for photosynthesis, can rapidly reach the inner cells of the leaf.
A network of veins extends throughout the leaf. Veins are made of the vascular tissues, xylem and phloem. Xylem transports water and mineral salts to the leaf cells. Phloem transports sugars away from the leaf cells to other parts of the plant. This maintains a concentration gradient so that the photosynthetic reactions proceed in the forward direction.
A waxy cuticle on the leaf epidermis protects the leaf by reducing evaporation of water. Water is an essential raw material for photosynthesis. Lack of water would also make the leaf wilt, reducing surface area for light absorption.
Stomata on the lower epidermis open in sunlight, allowing carbon dioxide to diffuse in and oxygen to diffuse out.
Mesophyll cells of the leaf contain numerous chloroplasts. Chloroplasts contain chlorophyll, which absorbs light energy for photosynthesis.
Mesophyll cells in the upper regions of the leaf (palisade mesophyll) contain more chloroplasts since more light energy can be absorbed near the leaf surface.
An interconnecting system of air spaces in the lower regions of the leaf (spongy mesophyll) allow rapid diffusion of carbon dioxide into mesophyll cells.
3. Discuss why the following statement is true: “Temperature will only increase the rate of photosynthesis to a certain extent. At very high temperatures, the rate of photosynthesis will decrease.”
Solution
Photosynthesis is an enzyme-catalysed reaction.
There will be increased collision of enzyme and substrate as temperature increases.
This results in more enzyme-substrate complex being formed and thus a greater rate of reaction. However, at very high temperatures, enzymes being protein in nature, will be denatured.
The substrate no longer fits into the active site and an enzyme-substrate complex cannot be formed.
Thus the rate of photosynthesis will decrease.
Diffusion & Osmosis in Cells
Plant and animal cells behave differently when exosmosis or endosmosis occurs, due to their structural differences:
1. Plant cells have a cell wall, which allows for only slight changes in size, and also prevents lysis of the cells.
2. Plant cells have large central vacuoles, which are not present in animal cells. Hence during osmosis, water moves between cell sap in central vacuole and the solution surrounding the cells. For animal cells, water moves between cytoplasm and the solution surrounding the cells.
Cell surface membranes affect the entry and exit of water and substances.
Factors that affect diffusion and osmosis are:
1. Surface area available: An increase in surface area leads to an increase in rate of diffusion and osmosis.
2. Permeability of membranes: Usually cell membranes are partially permeable. However, when membranes are exposed to organic solvents which dissolve the lipid bilayer (eg. ethanol or ether), or when cells are heated, the structure of the lipid bilayer is disrupted. This means that the membrane becomes fully permeable, which allows larger molecules inside the cell (eg. proteins) to diffuse out of the cell.
Points to Note for Structured Qn on Osmosis:
Turgid, Flaccid and Plasmolysis are terms used only for PLANT cells.
Instead, for a RBC, terms like haemolysis (bursting or lysis) and crenation (shrinkage) should be used.
Terms such as Exosmosis and Endosmosis should be used when referring to living cells only. The term Osmosis should be used when referring to experiments with non-living membranes such as visking tubings/dialysis tubings.
When referring to osmosis, use the term water potential, not water concentration as well as water potential gradient, not concentration gradient.
State specifically the shape of the RBC as being flattened and bi-concave.
If there is equal water potential in both cell and solution, state that the water potential gradient is zero resulting in no net movement of water molecules, thus no osmosis.
Use the template that is on the blog to help you phrase your answers!
1. Plant cells have a cell wall, which allows for only slight changes in size, and also prevents lysis of the cells.
2. Plant cells have large central vacuoles, which are not present in animal cells. Hence during osmosis, water moves between cell sap in central vacuole and the solution surrounding the cells. For animal cells, water moves between cytoplasm and the solution surrounding the cells.
Cell surface membranes affect the entry and exit of water and substances.
Factors that affect diffusion and osmosis are:
1. Surface area available: An increase in surface area leads to an increase in rate of diffusion and osmosis.
2. Permeability of membranes: Usually cell membranes are partially permeable. However, when membranes are exposed to organic solvents which dissolve the lipid bilayer (eg. ethanol or ether), or when cells are heated, the structure of the lipid bilayer is disrupted. This means that the membrane becomes fully permeable, which allows larger molecules inside the cell (eg. proteins) to diffuse out of the cell.
Points to Note for Structured Qn on Osmosis:
Turgid, Flaccid and Plasmolysis are terms used only for PLANT cells.
Instead, for a RBC, terms like haemolysis (bursting or lysis) and crenation (shrinkage) should be used.
Terms such as Exosmosis and Endosmosis should be used when referring to living cells only. The term Osmosis should be used when referring to experiments with non-living membranes such as visking tubings/dialysis tubings.
When referring to osmosis, use the term water potential, not water concentration as well as water potential gradient, not concentration gradient.
State specifically the shape of the RBC as being flattened and bi-concave.
If there is equal water potential in both cell and solution, state that the water potential gradient is zero resulting in no net movement of water molecules, thus no osmosis.
Use the template that is on the blog to help you phrase your answers!
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