Life Processes At A Cellular Level

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Movement of materials

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Materials such as oxygen, carbon dioxide, glucose, mineral ions and nutrients can be transported across the selectively permeable cell membrane through either passive or active transport.

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Passive transport

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Process does not need energy (ATP) as it follows the concentration gradient (molecules move randomly from an area of high concentration to an area of low concentration). Types of passive transport include diffusion, osmosis and facilitated diffusion.

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Active transport

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Process needs energy (ATP) as it travels against the concentration gradient. Types of active transport include proton pumps and cytosis - endocytosis and exocytosis.

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Diffusion

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Diffusion refers to the random movement of particles in liquids and gases resulting in a net movement from an area of high concentration to an area of low concentration and does not require energy (ATP). The higher the concentration gradient (the difference between the two concentrations in the two areas), the faster the rate of diffusion.

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Diffusion

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Diffusion refers to the random movement of particles in liquids and gases resulting in a net movement from an area of high concentration to an area of low concentration and does not require energy (ATP). The higher the concentration gradient (the difference between the two concentrations in the two areas), the faster the rate of diffusion.

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Other factors that affect the rate of diffusion

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1) size - small particles diffuse faster than larger ones

2) temperature - particles diffuse faster at higher temperatures than they do at low temperatures (more kinetic energy)

3) state - gas particles diffuse faster than particles in a liquid

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Diffusion

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Diffusion refers to the random movement of particles in liquids and gases resulting in a net movement from an area of high concentration to an area of low concentration and does not require energy (ATP). The higher the concentration gradient (the difference between the two concentrations in the two areas), the faster the rate of diffusion.

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Other factors that affect the rate of diffusion

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1) size - small particles diffuse faster than larger ones

2) temperature - particles diffuse faster at higher temperatures than they do at low temperatures (more kinetic energy)

3) state - gas particles diffuse faster than particles in a liquid

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Diffusion of small and large molecules

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Small molecules (e.g; O2, CO2, glucose) diffuse freely across membranes with the direction of movement being dependent on their concentration gradient. Large molecules (e.g; starch) are prevented from diffusing through the membrane.

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Facilitated diffusion

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Diffusion of specific particles through special transport or carrier proteins in the membrane. These transport proteins are specific, carrying only one type of molecule. Facilitated diffusion is a passive process because the molecules can only diffuse from high concentration to low concentration across the membrane.

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Facilitated diffusion

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Diffusion of specific particles through special transport or carrier proteins in the membrane. These transport proteins are specific, carrying only one type of molecule. Facilitated diffusion is a passive process because the molecules can only diffuse from high concentration to low concentration across the membrane.

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Osmosis

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Osmosis is a type of passive transport and is the movement of water across a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) until water potentials are equal.

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Facilitated diffusion

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Diffusion of specific particles through special transport or carrier proteins in the membrane. These transport proteins are specific, carrying only one type of molecule. Facilitated diffusion is a passive process because the molecules can only diffuse from high concentration to low concentration across the membrane.

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Osmosis

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Osmosis is a type of passive transport and is the movement of water across a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) until water potentials are equal.

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Hypotonic solution

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Weak or dilute solution (little dissolves solute)

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Facilitated diffusion

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Diffusion of specific particles through special transport or carrier proteins in the membrane. These transport proteins are specific, carrying only one type of molecule. Facilitated diffusion is a passive process because the molecules can only diffuse from high concentration to low concentration across the membrane.

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Osmosis

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Osmosis is a type of passive transport and is the movement of water across a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) until water potentials are equal.

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Hypotonic solution

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Weak or dilute solution (little dissolves solute)

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Hypertonic solution

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Strong or concentrated solution (much dissolved solute)

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Isotonic solution

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Two solutions with the same concentrations (I.e; same concentrations of water and solute)

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Proton or Ion Pump

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Active transport can be through the large proteins embedded in the phospholipid bilayer. The substance temporarily combines with the carrier protein, which changes shape (requires ATP to change shape) as it discharges the substance to the other side of the membrane. These carrier proteins are likely to be specific (carry only one particular substance).

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Cytosis

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Movement of large amounts of substances into/out of the cells by the folding of membranes. This causes a change in the shape of the cell and therefore requires ATP.

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Why do cells need to be small

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The size of cells (small) relates to their dependency on diffusion for getting substances into and out of the cell. When cells grow, their volume increases at a much faster rate than their surface area, as the volume increases as a cube factor while surface area increases as a square factor. As a cell grows, the ratio (SA:V) decreases and therefore there is comparatively less membrane for substances to diffuse the of and comparatively more organelles that need these substances. Diffusion gets less efficient and beyond a certain size, the centre of the cell does not receive the needed substances.

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Photosynthesis

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Process in which raw materials (water and carbon dioxide) are used to produce glucose and oxygen (oxygen being a waste product) in the presence of light energy and the pigment molecule, chlorophyll. Occurs within the chloroplasts of plant cells, mainly those of the lead and only during daylight hours. There are two main chemical pathways in this process and are both controlled by enzymes.

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Photosynthesis

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Process in which raw materials (water and carbon dioxide) are used to produce glucose and oxygen (oxygen being a waste product) in the presence of light energy and the pigment molecule, chlorophyll. Occurs within the chloroplasts of plant cells, mainly those of the lead and only during daylight hours. There are two main chemical pathways in this process and are both controlled by enzymes.

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Photosynthesis - light dependent reaction

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Light dependent reaction takes place on the thylakoids membranes of the grana of the chloroplasts. Chlorophyll embedded in the thylakoids membranes have their electrons 'excited' by solar energy striking them, to produce ATP. The electrons are then returned to the chlorophyll. Water is split into its constituent elements - hydrogen (H) and oxygen (O). Oxygen is not required in the rest of the photosynthesis process so is released as oxygen gas (O2). Hydrogen is picked up by a carrier molecule (NADP) and transferred to the light independent reaction in the stroma of the chloroplast.

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Photosynthesis - light independent reaction

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Light independent reaction (also known as the Calvin cycle) occurs in the stroma of the chloroplast. The CO2 and H enter a complex biochemical cycle and join together to form glucose (C6H12O6). ATP (produced in the light dependent reaction) is used to run the cycle.

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Photosynthesis - light independent reaction

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Light independent reaction (also known as the Calvin cycle) occurs in the stroma of the chloroplast. The CO2 and H enter a complex biochemical cycle and join together to form glucose (C6H12O6). ATP (produced in the light dependent reaction) is used to run the cycle.

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Rate of photosynthesis

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Rate of photosynthesis is determined by factors such as temperature, light intensity and carbon dioxide concentration.

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Photosynthesis - light independent reaction

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Light independent reaction (also known as the Calvin cycle) occurs in the stroma of the chloroplast. The CO2 and H enter a complex biochemical cycle and join together to form glucose (C6H12O6). ATP (produced in the light dependent reaction) is used to run the cycle.

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Rate of photosynthesis

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Rate of photosynthesis is determined by factors such as temperature, light intensity and carbon dioxide concentration.

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Rate of photosynthesis - temperature

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Increasing the temperature increases rate of photosynthesis up to an optimum temperature. When temperatures rise too far above the optimum temperature, the enzymes controlling the reactor denature and can no longer catalyse the reaction as the substrate doesn't fit into the active site. Therefore photosynthesis ceases.

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Rate of photosynthesis - light intensity

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Increasing the light intensity increases the rate of photosynthesis up to a maximum. Above this maximum, further increases in light have no further effect on the photosynthetic rate (because either the light-absorbing pigments are saturated and/or the concentration of CO2 and/or temperature is low (also limiting)

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Rate of photosynthesis - CO2 concentration

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Increasing CO2 concentration increases the rate of photosynthesis up to a maximum. Above this max CO2 concentration, further increases in CO2 concentration have no further effect on the photosynthetic rate (because the Calvin cycle is saturated and/or the amount of light intensity is limiting the light dependent reactions and/or temperature is low.

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Other environmental factors that can influence rate of photosynthesis

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1) water concentration - cell will close stomata to prevent water loss when dehydrated, closing of the stomata will also prevent entry of CO2 which will limit photosynthesis

2) mineral ions - certain mineral ions are essential for photosynthesis to occur (Mg)

3) light wavelength - light absorbing pigments are most active when absorbing he blue and red wavelengths, green wavelengths are reflected instead of absorbed

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Other environmental factors that can influence rate of photosynthesis

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1) water concentration - cell will close stomata to prevent water loss when dehydrated, closing of the stomata will also prevent entry of CO2 which will limit photosynthesis

2) mineral ions - certain mineral ions are essential for photosynthesis to occur (Mg)

3) light wavelength - light absorbing pigments are most active when absorbing he blue and red wavelengths, green wavelengths are reflected instead of absorbed

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Respiration

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Respiration is the process in which the cell breaks down glucose to produce ATP, occurs in the mitochondria. Breakdown of glucose may be aerobic or anaerobic; aerobic respiration produces much larger amounts of ATP per glucose molecule than anaerobic respiration does

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Other environmental factors that can influence rate of photosynthesis

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1) water concentration - cell will close stomata to prevent water loss when dehydrated, closing of the stomata will also prevent entry of CO2 which will limit photosynthesis

2) mineral ions - certain mineral ions are essential for photosynthesis to occur (Mg)

3) light wavelength - light absorbing pigments are most active when absorbing he blue and red wavelengths, green wavelengths are reflected instead of absorbed

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Respiration

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Respiration is the process in which the cell breaks down glucose to produce ATP, occurs in the mitochondria. Breakdown of glucose may be aerobic or anaerobic; aerobic respiration produces much larger amounts of ATP per glucose molecule than anaerobic respiration does

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ATP

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Energy molecule used to fuel all the chemical reactions of the cell

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Aerobic respiration

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Aerobic respiration needs oxygen for the complete breakdown of glucose into carbon dioxide and water; energy is released in the form of ATP and heat. Three main enzyme-controlled stages in aerobic respiration - glycolysis, Krebs cycle and the electron transfer chain.

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Respiration - glycolysis

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Occurs in the cytoplasm of cell, each glucose molecule is broken down into two pyre ate molecules and two molecules of ATP are produced in the breakdown

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Aerobic respiration - glycolysis

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Occurs in the cytoplasm of cell, each glucose molecule is broken down into two pyre ate molecules and two molecules of ATP are produced in the breakdown

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Aerobic respiration - Krebs cycle

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Second stage of aerobic respiration, occurs in the matrix of the mitochondria. Pyruvate molecules are fed into a complex biochemical cycle. As it passes around the cycle, extensive rearrangement occurs with CO2 molecules and H atoms being produced. The molecules that make up the cycle are not used up in the reaction. CO2 are the waste products and diffuse out of the mitochondria and cell. H atoms are picked up by a carrier molecule (NADP) and taken to third stage of aerobic respiration.

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Aerobic respiration - electron transfer chain/respiratory chain

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Final stage, occurs on the cristae of mitochondria. The hydrogen atoms are passed along the electron transfer chain, releasing energy which is captured as ATP. Each glucose molecules produces 38 molecules of ATP by the end of aerobic respiration.

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Aerobic respiration - electron transfer chain/respiratory chain

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Final stage, occurs on the cristae of mitochondria. The hydrogen atoms are passed along the electron transfer chain, releasing energy which is captured as ATP. Each glucose molecules produces 38 molecules of ATP by the end of aerobic respiration.

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Anaerobic respiration

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Occurs when there is limited oxygen, only glycolysis occurs. The pyruvate molecules formed in glycolysis are broken down into lactic acid. This buildup of lactic acid causes muscle fatigue. This small energy yield of 2 ATP is sufficient to meet lifestyle of organisms like bacteria and yeast.

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Rate of respiration - temperature

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Increasing the temperature increases the rate of respiration up to an optimum temperature. As temperatures rise too high above the optimum temperature, the enzymes controlling the reaction denature and can no longer catalyse reactions; respiration ceases.

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Rate of respiration - body's energy demands

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The rate of respiration will increase up to a max as the demand from the cells of tissues increases. The amount of O2 needed and the amount of CO2 produced increase and therefore the breathing rate needs to compensate. The build-up of CO2 will slow down the rate of respiration.

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Enzymes

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Act as biological catalysts as they speed up the chemical reactions involved in life processes

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Enzymes

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Act as biological catalysts as they speed up the chemical reactions involved in life processes

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Anabolic reactions

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Reactions that synthesise (produce) large molecules from smaller ones

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Enzymes

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Act as biological catalysts as they speed up the chemical reactions involved in life processes

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Anabolic reactions

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Reactions that synthesise (produce) large molecules from smaller ones

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Catabolic reactions

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Reactions that break down large molecules into smaller ones

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Enzymes

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Act as biological catalysts as they speed up the chemical reactions involved in life processes

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Anabolic reactions

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Reactions that synthesise (produce) large molecules from smaller ones

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Catabolic reactions

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Reactions that break down large molecules into smaller ones

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Enzymes are specific

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Enzymes only catalyse one type of reaction

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Enzymes

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Act as biological catalysts as they speed up the chemical reactions involved in life processes

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Anabolic reactions

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Reactions that synthesise (produce) large molecules from smaller ones

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Catabolic reactions

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Reactions that break down large molecules into smaller ones

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Enzymes are specific

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Enzymes only catalyse one type of reaction

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Reason that enzymes are specific

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Each enzyme has a particular shape, determined by its sequence of amino acids. The shape of the enzyme in an area known as its active site corresponds to that of the substance it catalyses. The substrate fits into the active site of the enzyme such as a key fits into a lock. As the enzyme and substrate fit together (forming the enzyme-substrate complex) with the substrate being held to the active site through hydrogen bonds. The enzyme's active site changes its shape slightly through the weak hydrogen bonds when combined with the substrate to distort the substrate molecules, making the reaction more likely.

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Denaturing of enzymes

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Enzymes are not consumed or broken down in a reaction so one enzyme molecule can catalyse he same reaction many times at a very fast rate. Because their shape is maintained by weak hydrogen bonds, enzymes are susceptible to denaturing at high temperatures. As the hydrogen bonds are broken and the enzyme loses its shape, it can no longer catalyse the reaction.

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Denaturing of enzymes

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Enzymes are not consumed or broken down in a reaction so one enzyme molecule can catalyse he same reaction many times at a very fast rate. Because their shape is maintained by weak hydrogen bonds, enzymes are susceptible to denaturing at high temperatures. As the hydrogen bonds are broken and the enzyme loses its shape, it can no longer catalyse the reaction.

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Factors that affect enzyme activity - temperature

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The warmer the temperature, the faster enzymes catalyse a reaction. This is because increasing he temperature increases the speed at which the reacting particles move, so they collide more often. It is necessary for participles to collide for them to react. However, above 40-45 degrees, enzymes are usually denatured and can no longer catalyse the reaction. The temperature at which the reaction rate is the fastest is the optimum temperature.

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Denaturing of enzymes

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Enzymes are not consumed or broken down in a reaction so one enzyme molecule can catalyse he same reaction many times at a very fast rate. Because their shape is maintained by weak hydrogen bonds, enzymes are susceptible to denaturing at high temperatures. As the hydrogen bonds are broken and the enzyme loses its shape, it can no longer catalyse the reaction.

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Factors that affect enzyme activity - temperature

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The warmer the temperature, the faster enzymes catalyse a reaction. This is because increasing he temperature increases the speed at which the reacting particles move, so they collide more often. It is necessary for participles to collide for them to react. However, above 40-45 degrees, enzymes are usually denatured and can no longer catalyse the reaction. The temperature at which the reaction rate is the fastest is the optimum temperature.

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Factors that affect enzyme activity - pH

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For many enzymes, their optimum pH is approximately 7 as they work within cells. When the pH is outside the range for an enzyme, the enzyme denatures and can no longer act as a catalyst. As a result, the substrate won't be able to fit into the active site. Once an enzyme has denatured, it won't function again.

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Factors that affect enzyme activity - substrate concentration

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The rate of enzyme activity will increase as the concentration of the substrate increases up until a saturation point occurs (no free enzymes). When this saturation point occurs, there is no further increase in reaction rate.

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Factors that affect enzyme activity - substrate concentration

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The rate of enzyme activity will increase as the concentration of the substrate increases up until a saturation point occurs (no free enzymes). When this saturation point occurs, there is no further increase in reaction rate.

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Factors that affect enzyme activity - co-factors

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A co-factor is a non-protein chemical compound that is required for the enzyme to function properly (e.g; cobalt and selenium). Co-factors generally sit in the enzyme active site and assist the bonding of the substrate. They are necessary when only weak bonds form between the enzyme and the substrate; the co-enzyme acts as a bridge, locking the enzyme and substrate more tightly together.

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Factors that affect enzyme activity - substrate concentration

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The rate of enzyme activity will increase as the concentration of the substrate increases up until a saturation point occurs (no free enzymes). When this saturation point occurs, there is no further increase in reaction rate.

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Factors that affect enzyme activity - co-factors

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A co-factor is a non-protein chemical compound that is required for the enzyme to function properly (e.g; cobalt and selenium). Co-factors generally sit in the enzyme active site and assist the bonding of the substrate. They are necessary when only weak bonds form between the enzyme and the substrate; the co-enzyme acts as a bridge, locking the enzyme and substrate more tightly together.

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Factors that affect enzyme activity - inhibitors

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Inhibitors are substances that prevent enzymes catalysing reactions. An inhibitor can be competitive or noncompetitive. Competitive inhibitors bind to the active site and prevent the substrate from binding to the active site (this inhibition can be overcome by adding excess substrate). Non-competitive inhibitors bond to another part of the shape and alter the shape of the active site so that it can no longer bind to a substrate. Heavy metals such as mercury and cadmium often act as non-competitive inhibitors.

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DNA

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Molecule in chromosomes that carries the genetic code, its shape is a double helix. Side strands age made of alternating sugar and phosphate groups, cross strands are the paired bases.

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Nucleotide

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Nucleotide is made of three parts; a deoxyribose sugar, a phosphate group and a nitrogen base. Only difference between nucleotides is the base they contain.

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Importance of DNA replication

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It's essential that DNA can replicate itself so that the chromosomes can be copied to give the same genetic code to every new cell that is made. It is the base pairing mechanism that allows DNA to replicate. This process is enzyme controlled with energy supplied from ATP. Two identical DNA molecules result from replication, each having one original strand and one new strand, known as semi conservative replication.

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Antiparallel

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The two sides of DNA run in opposite directions

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DNA replication process

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Enzyme DNA helicase unwinds the DNA helix, exposing the base pairs. Enzyme DNA polymerase joins new bases (nucleotides) to the existing strand. DNA polymerase is unable to begin adding bases to a new strand from scratch so RNA primer is needed to start replication. This primer was later removed. DNA polymerase can only bond nucleotides directly down the entire length of the 3"-5" strand. This is known as the leading strand in DNA replication. The other strand (running 5"-3") must be copied in short fragments of approximately 1000 bases called Okazaki fragments. This is known as the lagging strand. Enzyme ligand bonds the Okazaki fragments to form a continuous strand. The DNA helix is opened at many sites along the whole molecule for simulateous replication otherwise replication would be too slow.

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Results of DNA replication

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Two identical DNA molecules are formed. DNA replication occurs prior to cell division during interphase.

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Results of DNA replication

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Two identical DNA molecules are formed. DNA replication occurs prior to cell division during interphase.

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Mitosis

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Cell division for growth and repair, process produces two daughter cells genetically identical to the parent cell. Takes place most rapidly when new cells are forming during periods of growth. Rate of mitosis is influenced by factors such as temperature, the availability of essential nutrients and the presence of mutagens.

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Stages of Mitosis

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Chromosomes replicate to form two chromatids. Chromosomes shorten and thicken. The nuclear membrane disappears. The chromatids are held together by centromeres. Spindle fibres develop from the centrioles. The spindle fibres twist and turn the chromatids, lining them up along the cell equator. The centromeres split and the individual chromatids move towards the cell poles, pulled by the forces acting on the spindle fibres. The chromatids arrive at the cell's poles. Nuclear membranes begin to form around each group of chromatids. The plasma membrane begins to constrict between them. The daughter cells will grow then repeat the mitosis process again. The two new cells will have exactly the same number of chromosomes as each other and as the parent cell, genetically identical.

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Mitochondria

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Site of aerobic respiration, elongated ovals in shape and their inner membrane is thrown up into folds called cristae. Cristae provide a large surface for the hydrogen transfer chain to take place. Having a large surface area enables effective production of ATP. In cells with a large demand for ATP, mitochondria contain even more cristae to increase surface area, so maximising production of ATP. Space between cristae known as matrix.

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Chloroplast

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Site of photosynthesis, within chloroplast are flattened membranes called thylakoids arranged in stacks called grana. Embedded in these membranes are chlorophyll molecules which absorb solar energy. Thylakoids provide a large surface area for the light dependent chemical reactions of photosynthesis. Between the grana is the fluid matrix known as the stroma - where the light independent reaction takes place