3.7.1 Define cell respiration. Cell respiration is the controlled release of energy from organic compounds in cells to form ATP.

All living things need energy to stay alive. The energy is used to power all the activities for life including digestion, protein synthesis, and active transport.

A cell’s energy sources are sugars and other substances taken from nutrients, which can be broken down to release the energy that is stored in the bonds.

Aerobic cell respiration:glucose + oxygen carbon dioxide + water + energy

Cellular respiration is the gradual breakdown of nutrient molecules such as glucose and fatty acids in a series of reactions that release energy in the form of ATP.

Glycolysis

The first stage in cellular respiration is glycolysis. Glucose that is present in the cytoplasm of a cell is broken down by a series of enzymes, to produce 2 molecules of a simpler compound- pyruvate

As this occurs there is a net production of 2 ATP moleculesGlucose 2 pyruvate + ATP

http://www.youtube.com/watch?v=3GTjQTqUuOw

3.7.2: State that, in cell respiration, glucose in the cytoplasm is broken down byglycolysis into pyruvate, with a small yield of ATP.

IB Question: In the cytoplasm of the cell, glucose is broken down into pyruvate in a process called glycolysis. State one product of glycolysis. [1]

ATP / NADH + H+ / 2 NADH / reduced NAD [1]

Aerobic Respiration

The next stage of cell respiration depends on whether there is oxygen present or not.

Aerobic respiration- with oxygenAnaerobic respiration- without oxygen

Aerobic respiration is the most effective way of producing ATP.

Aerobic respiration is carried out by cells in the mitochondria and it produces a large amount of ATP.

Pyruvate molecules produced by glycolysis enter the mitochondria and are broken down, or oxidized, in a series of reactions that release CO2 and H2O and produce ATP

Krebs Cycle

The two pyruvate molecules from glycolysis first lose carbon dioxide and become 2 molecules of acetyl CoA

Acetyl CoA then enters the Krebs Cycle and is modified further releasing carbon dioxide.

Products of the cycle react with oxygen and result in the release of large amounts of ATP.Glucose+ O2 CO2 + H2O + 38 ATP net result of 36ATP

http://www.youtube.com/watch?v=ClXcQ0WFjkk

3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP

Anaerobic Respiration

Anaerobic respiration occurs in the cytoplasm of cells.

In animal cells the pyruvate produced by glycolysis is converted to lactate, which is a waste product of cells.

When exercising rigorously the cardiovascular system is unable to supply the muscles with enough oxygen, resulting in cramps and muscle soreness.

In other organisms, such as yeast, anaerobic respiration is known as fermentation and produces a different outcome.

The pyruvate molecules are converted to enthanol (alcohol) and carbon dioxide.

No further ATP is produced in anaerobic respiration.

IB Question: List two end products of aerobic cell respiration. [2]

aerobic respiration;

Carbon dioxide , water, ATP

IB QUESTION: Distinguish between the process of anaerobic respiration in yeast and humans. [2]

yeast: pyruvate to ethanol and carbon dioxide; humans: pyruvate to lactic acid; [2] Award [1 max] if products are appropriately linked to organisms without the mention of pyruvate.

3.7.4 Explain that, during aerobic cell respiration, pyruvate can be brokendown in the mitochondrion into carbon dioxide and water with a large yield of ATP.

IB Question: Using a table, compare aerobic and anaerobic respiration in a eukaryotic cell. [5]

Award [1] for each correct row, up to [5 max].Aerobic respiration Anaerobic respirationoccurs in mitochondria occurs in cytoplasm;requires 2 O occurs without 2 O ;both produce pyruvate from glucose (glycolysis);uses fatty acids/lipids/amino acids doesn’t use fatty acids;(Krebs cycle) produces CO2 and H2 O (fermentation) produces ethanol / CO2(in yeast) ;(Krebs cycle) produces CO2 and H 2O (fermentation) produces lactate inanimals (humans) ;NADH produced in both;large amount of ATP (36 per glucosemolecule) producedsmall amount of ATP (2 per glucosemolecule) produced; [5 max]

IB Question: Explain the process of aerobic cell respiration. [8]

cell respiration produces energy;controlled release of energy;by breakdown of organic molecules/glucose;energy from them is used to make ATP;aerobic respiration is in mitochondria;requires oxygen;pyruvate is produced by glycolysis / glucose broken down;pyruvate is broken down in the mitochondria;into carbon dioxide and water;large production of ATP;per molecule/mass of glucose;much higher production of ATP than in anaerobic respiration; [8 max]

IB Question: Compare anaerobic cellular respiration and aerobic cellular respiration. [5]

Direct comparisons must be made to achieve a mark.anaerobic in the absence of oxygen whereas aerobic in the presence of oxygen;both may produce 2 CO ;both produce ATP;aerobic releases considerably more ATP per glucose molecule than anaerobic;anaerobic/fermentation in plants produces alcohol / anaerobic in animals produceslactic acid neither produced in aerobic respiration;glucose can be the substrate for both;glucose can be the substrate for both;anaerobic entirely in cytoplasm whereas aerobic requires mitochondria/specializedregion of membrane;glucose is broken down into pyruvate in the cytoplasm in both; [5 max]

3.8: Photosynthesis

carbon dioxide + water glucose + oxygen

http://www.youtube.com/watch?v=C1_uez5WX1o

http://www.youtube.com/watch?v=LgYPeeABoUs

The sun is the source of energy for almost all life on Earth

3.8.1 State that photosynthesis involves the conversion of light energy into chemical energy.

Light energy from the Sun is captured by plants and other photosynthetic organisms, and converted into stored chemical energy.

The energy is stored in molecules such as glucose, which provide a source of food for organisms that cannot use light energy directly

Visible light is composed of a spectrum of colors, which can be separated using a prism.

A prism bends rays of light and separates the colors because each one has a slightly different wavelength, and is bent at a different angle.

Most important regions of visible light are red and blue for photosynthesis

3.8.2 State that light from the Sun is composed of a range of wavelengths (colours).

The color of any object is determined by the wavelength of the light it reflects back into your eyes.

A blue shirt appears blue because it reflects blue light, which our eyes can perceive, but it absorbs other wavelengths that fall on it and we don’t see those colors.

A black shirt will absorb all wavelengths of light, while a white one will reflect them all.

Most plants have green leaves. They do not absorb the green part of the spectrum, green light is reflected making the leaf appear green.

chloroplast

The green color is due to the chloroplasts, which contain a green pigment called chlorophyll.

Chlorophyll is unable to absorb green light, which it reflects, but it absorbs other wavelengths well. Red and blue light are absorbed particularly well and provide the energy needed for photosynthesis.

3.8.4: Outline the differences in absorption of red, blue and green light bychlorophyll.

3.8.3 State that chlorophyll is the main photosynthetic pigment.

The Chemistry of Photosynthesis

• Photosynthesis is a complex series of reactions catalyzed by a number of different enzymes.

• Photosynthesis can be split into 2 stages: Light-dependent reactions and Light- independent reactions.

Light-dependent reactions• The first stage is called light-dependent reactions because

light is essential for them to occur.

• Chlorophyll absorbs light energy and this energy is used to produce ATP.

• Energy is used to split water molecules into hydrogen and oxygen is a process called photolysis.

Hydrogen ions, electrons, and oxygen are released. Oxygen is released as a waste product (good for us!!)

The ATP, hydrogen ions and electrons are used in the light independent reactions.

http://www.youtube.com/watch?v=v590JJV96lc

Light-independent reactions• During the light independent reactions carbon dioxide (CO2), taken in

from the air, is combined with hydrogen and ATP to form a range of organic molecules for the plant.

• The conversion of inorganic carbon dioxide to organic molecules such as glucose is called carbon fixation.

• ATP provides the energy for the process.

http://www.youtube.com/watch?v=E_XQR800AgM&feature=related

Summary of Photosynthesis

6

six

Measuring the Rate of Photosynthesis

The equation shows that when photosynthesis occurs, carbon dioxide is used and oxygen is released.

The mass of the plant (its biomass) will also increase as glucose is used to produce other plant materials.

3.8.7 Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.

Aquatic plants release bubbles of oxygen as they photosynthesize and if the volume of these bubbles is measured for a period of time, the rate of photosynthesis can be determined directly.

Aquatic plants also remove carbon dioxide from the environment, causing the pH of the water to rise. Carbon dioxide dissolves in water to a form a weak acid so as it is removed, the pH will go up.

Another way to determine the rate of photosynthesis is to monitor the change in pH of the surrounding water over time.

Indirect Method

A thirds method of measuring the rate of photosynthesis in plants is to determine their biomass at different times.

Samples of the plants can be collected and measured at different times and the rate of increase in their biomass calculated to determine the rate of photosynthesis.

Limits of Photosynthesis

The rate of photosynthesis depends on factors in the environment.

On a warm, sunny afternoon, photosynthesis will be more rapid than on a cold, cloudy morning.

More oxygen will be produced and more carbon dioxide used.

Limiting FactorsPhotosynthesis cannot increase beyond certain limits

Light, temperature, and carbon dioxide are limiting factors involved in photosynthesis.

Effect of light intensity on rate of photosynthesis

An increase in light intensity, when all other variables are the same, will produce an increased rate of photosynthesis. However, at a certain light intensity enzymes will be working at maximum rate, limited by temperature and availability of CO2

3.8.8: Outline the effects of temperature, light intensity and carbon dioxideconcentration on the rate of photosynthesis.

Effect of Temperature on rate of photosynthesis

Increasing temperature also increases the rate of photosynthesis as the frequency and energy of molecular collisions increases. Photosynthesis has an optimum temperature above it the rate decreases sharply as enzymes are denatured, or the plant wilts and is unable to take in CO2

Effect of carbon dioxide concentration on rate of photosynthesis

An increase in the concentration of CO2 causes the rate of photosynthesis to increase, as CO2 is a vital raw material for the process. AT very high concentrations, the rate will plateau as other factors such as light and temperature limit the rate of the reaction.

The effects of temperature, light, and CO2 concentrations are well known to farmers who grow crops in greenhouses.

Commercial producers of cucumbers and tomatoes keep their greenhouses warm and well lit. They may also introduce CO2 to boost the photosynthesis to maximum rate, thereby increasing crop production and profits.

IB Question: i. State the principal conversion of energy that occurs in photosynthesis. [1]

ii. State the molecule necessary for this conversion of energy.

(i) light (energy) to chemical (energy)/ATP/glucose/NADPH/sugar; [1](ii) chlorophyll [1]

[1]

IB Question: Outline the difference in absorption of red, blue and green light by chlorophyll for the process of photosynthesis. [1]

red and blue light is absorbed and green light is reflected / blue light is absorbedthe most and green light is absorbed the least [1]

IB QUESTION: Outline how light energy is used and how organic molecules are made in photosynthesis. [6]

chlorophyll is the (main) photosynthetic pigment;absorbs (mainly) red and blue light;green light is reflected;light energy absorbed is converted into chemical energy;ATP produced;water split;to form oxygen and hydrogen;ATP and hydrogen used to fix carbon dioxide to make organic molecules; [6 max]

IB Question: Explain how the rate of photosynthesis can be measured. [5]

rate can be measured by the disappearance of raw materials / 2 CO (in solution);rate of change of 2 CO can be measured (indirectly) by pH change;rate can be measured by the appearance of products/ 2 O /starch;rate can be measured by measuring rate of change of biomass;description of apparatus to measure the rate of photosynthesis / annotated diagram;explanation of expected experimental outcome: e.g. increased photosynthesis inan aquatic plant – more 2 O bubbles counted per unit time; [5 max]

IB Question: Explain how photosynthesis can be measured both directly and indirectly. [3]

(a) directly:by production of oxygen / measuring thevolume/number of bubbles of gas produced;by measuring the uptake of carbon dioxide;changes in pH;Do not accept “production of gas”.indirectly:by measuring the increase in biomass;by measuring the production of glucose / starch / other suitable molecule; [3 max]Award [2 max] if only indirect measurements or direct measurements are addressed.Apply ECF if direct and indirect is confused for more than one method.

IB Question: Outline how three different environmental conditions can affect the rate of photosynthesis in plants. [6]

light: [2 max] rate increases with increasing light; it reaches maximum then plateaus; as all chloroplast molecules are working at optimal pace; temperature: [2 max] rate increases with increasing temperature; to a maximum/optimum temperature; but then falls off rapidly; as enzymes are denatured above the optimal temperature; carbon dioxide: [2 max] rate increases with increasing carbon dioxide level; it reaches maximum then plateaus; as photosynthesis operating at optimal level; [6 max] Award any of the above points if clearly drawn in a diagram.

IB Question: Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis. [6]

Award credit for the following points if annotated on sketched graphs.all three variables can be classified as limiting factors;as temperature increases, photosynthetic rate increases;maximum rate of photosynthesis at optimum temperature;at (very) high temperatures photosynthesis slows/stops;as light intensity increases, photosynthetic rate increases;at high light intensity, photosynthesis stops increasing;minimum light intensity necessary for photosynthesis to occur;(because concentration is rarely high) 2 CO is the main rate-limiting variable;as concentration of 2 CO rises, photosynthetic rate rises (up to a certain point); [6 max]