Cells 2 Flashcards
Cell Composition
All living cells are made up of seven types of substances: water carbohydrates fats and oils (lipids) proteins minerals vitamins and nucleic acids (fig. 11-1)
Cellular Need
The most important need of a cell is to get these materials for its growth and reproduction
Metabolic Reactions
The numerous metabolic reactions that occur inside a living cell arise from this need
Anabolic Reactions
The anabolic reactions which give rise to growth and reproduction require energy
Catabolic Reactions
This is released in catabolic reactions (see page 38)
Metabolic Reaction Importance
These metabolic reactions are essential for life If they stop the cell dies
Multicellular Organism Properties
Basically the properties and functions of a multicellular organism are the sum total of the properties and functions of its constituent cells
Plant and Animal Cell Composition
Plants and animals are made up of cells Since all cells contain protoplasm and cell membrane the nutrients they need for their activities growth and reproduction are similar
Amoeba Nutritional Needs
NOTE The nutritional needs of an Amoeba would of course be very much less complex than that of a human being-just compare all the organs a human has with the organelles of an Amoeba!
Specialized Cell Nutritional Needs
Again the nutritional needs of specialized cells in an organism will vary according to their structural adaptations and functions
Red Blood Cell Needs
For example the red blood cell needs iron for its function while the cells in the skin do not
Major Elements
Table 11-1 gives the essential nutrient elements needed by most living organisms The major elements are those that are needed in large amounts while the trace elements are needed in very small amounts (a few parts per million)
Green Plant Elements
Green plants get the elements carbon hydrogen and oxygen from carbon dioxide and water and the rest as mineral salts from their environment
Organic Material Synthesis
Using these they synthesize the organic materials that they need mainly carbohydrates proteins lipids vitamins and nucleic acids
Animal Essential Elements
Animals get all the essential elements from ready-made food This food in turn is made up of plant and/or animal parts and products The main organic substances in food are carbohydrates proteins and lipids
Macronutrients
They are known as macronutrients They supply the elements carbon hydrogen oxygen nitrogen and phosphorus
Micronutrients
The remaining major essential elements are needed in smaller amounts These together with the trace elements and the vitamins are usually known as micronutrients
Vitamins
Vitamins are essential organic substances that are needed by animals in trace amounts for the healthy functioning of their cells Plants can synthesize vitamins in their cells
Nutrient Deficiency Effect
Lack of any essential nutrient in the diet of an organism affects its cells
Lack of Iron Effect
For example lack of iron in a human diet means red blood cells cannot function properly This causes anaemia a deficiency condition
Green Plant Deficiency
In the case of green plants the cells cannot synthesize chlorophyll This affects their food-making process Deficiency is seen in the yellowing of leaves and poor growth of the plant
Direct Effect of Deficiency
Thus we see that the direct effect of nutritional deficiency is on the relevant cells of the organism
Organism Deficiency
Eventually the organism as a whole is affected and is said to suffer from a deficiency disease or condition
Too Much Nutrients
Too much nutrients may also harm an organism For example a person who eats too much carbohydrates and fats becomes obese
Obesity Cause
This is due to the formation and accumulation of fat storage cells in the body
High Protein Diet Effect
A very high protein diet overworks the cells in the liver and kidney as they have to break down the nutrients and excrete them These organs as a whole become damaged causing early deterioration Excess of certain micronutrients also have similar effects on the cells of a person
Mineral Nutrient Effect on Plants
We can also observe the effects of too much mineral nutrients on plants by adding a concentrated solution of an inorganic fertilizer to a growing plant The plant wilts and dies as the strong solution causes the root hair cells to plasmolyse
Cellular Respiration
All living cells need energy for the metabolic processes essential for life They get this from the chemical energy stored in food Autotrophic plant cells get their energy from the food they make while heterotrophic animal cells get it from the food they ingest
Food Energy Demonstration
We can show that food contains energy by burning some food in oxygen For example when a maize cob is burnt the energy in it is set free as heat and light
Food Energy Measurement
We can measure the energy in food accurately by using a food calorimeter In this device a known mass of food is burnt as shown in fig 11-2 The heat released warms the water in the calorimeter From the rise in temperature of the water we can calculate the amount of energy in the food sample
Energy-Rich Nutrients
The energy-rich nutrients in food are carbohydrates lipids and proteins Their energy contents are as follows
Carbohydrate Energy
1 g contains 16-7 kJ
Fats Energy
1 g contains 37-6 kJ
Proteins Energy
1 g contains 16-7 kJ
Food Burning Reaction
When food is burnt in the laboratory the following reaction occurs: food + oxygen → carbon dioxide + water + energy
Oxygen’s Role
Oxygen is necessary for food to burn It is therefore an oxidation reaction The complex food substance is broken down to liberate the simpler molecules carbon dioxide and water and energy The reaction is rapid and heat is given off in large amounts in one big step
Cellular Burning Process
Scientists have shown that food is also burnt in a similar way in living cells The main food that is burnt in cells is glucose This oxidation process produces energy carbon dioxide and water as summarized below: $C_{6}H_{12}O_{6} + 6O_{2} → 6CO_{2} + 6H_{2}O + energy$
Energy Release Steps
However the energy is not released in one step as shown in the above reaction but in a series of small steps which are catalysed by enzymes The energy that is released bit by bit is stored in adenosine triphosphate (ATP) molecules The oxidation of glucose to release energy in this manner is known as cellular respiration It occurs in the mitochondria of all living cells
Cellular Respiration Steps
The main steps in cellular respiration are shown in fig 11-3 One molecule of the 6-carbon glucose is broken down into two molecules of the 3-carbon pyruvic acid by enzymes in the cytoplasm of the cell These reactions do not require oxygen Each molecule of pyruvic acid is oxidized completely to carbon dioxide and water in the mitochondrion This latter series of reactions is known as the Kreb’s cycle Most of the ATP molecules is formed in this cycle A total of thirty-eight ATP molecules are formed when one molecule of glucose is completely oxidized When needed lipids and proteins are broken down to small molecules and enter the Kreb’s cycle at various points
ATP and Glucose
Glucose the substrate in cellular respiration and ATP the final essential end product are both molecules that act as energy stores
Why Cellular Respiration?
So why does the cell go through the elaborate process of cellular respiration?
Glucose Stability
Glucose is a stable compound which will not release energy quickly and easily as and when it is needed for the cell’s activities
ATP Reactivity
ATP however is an extremely reactive compound which will release its energy quickly when it is needed as shown: $ATP + H_{2}O → ADP + phosphoric acid + energy$ Energy is released simply by the breaking off of a phosphate group from ATP Thus ATP is the cell’s immediate energy store
Glucose’s Role
Glucose is an ideal substance for transferring energy from the organism’s energy stores to the individual cells
Other Molecule Roles
Other larger molecules like starch glycogen and fats are ideal for acting as long term energy stores within an organism; and transferring energy from one organism to another (in the food of heterotrophs)
Aerobic Respiration
In most cells cellular respiration occurs in the presence of oxygen This is known as aerobic respiration The largest number of ATP molecules is formed from one molecule of glucose in this process
Anaerobic Respiration
In some organisms the cells get energy by breaking down glucose in the complete absence of oxygen This is known as anaerobic respiration
Alcoholic Fermentation
In the cells of certain bacteria in fungi like yeast and in cells of plant parts like germinating seeds glucose is partially broken down to pyruvic acid This acid is then converted to ethanol Since the end product is an alcohol the process is known as alcoholic fermentation: $C_{6}H_{12}O_{6} → 2CH_{3}CH_{2}OH + 2CO_{2} + energy$
Alcoholic Fermentation Commercial Importance
Alcoholic fermentation is of great importance commercially in breweries Here yeast breaks down materials rich in carbohydrates to produce ethanol in the absence of oxygen
Anaerobic Respiration in Animal Cells
In animal cells that are respiring anaerobically the pyruvic acid from glucose is converted to lactic acid instead: $\begin{matrix}C_{6}H_{12}O_{6} → 2CH_{3}CH(OH)COOH + energy \ glucose \ lactic \ acid \end{matrix}$
ATP Yield in Anaerobic Respiration
In anaerobic respiration each molecule of glucose yields only two ATP molecules Compare this with the thirty-eight molecules obtained in aerobic respiration!
Cytoplasm in Anaerobic Resiration
In the cytoplasm Two molecules of ATP are needed to begin the process Each stage is catalysed by an enzyme e.g. a molecule decarboxylase removes $CO_{2}$ from a molecule After the production of glycerate-3-phosphate the number of ATP molecules are doubled Each molecule of glycerate - 3 phosophate gives rise to 20 molecules of ATP Do not forget to take away the two ATPS at the start So the total number of ATPS from one molecule of glucose is 38 $(40-2)$ Count the ATPS in the diagram Account for each ATP in the 38 total
Mitochondria
In the mitochondria The prodution of hydrogen atoms during the process can be monitored using DCPIP (Dichlorophenol indophenol) It is hydrogen acceptor and become colourless when fully reduced
Oxygen Debt
All the cells in the body need oxygen for respiration and all this oxygen is supplied by the lungs The oxygen is carried by the blood to every part of the body Sometimes cells may need a lot of oxygen very quickly During vigorous exercise the muscles of the legs are using up a lot of enery To produce this energy the mitochondria in the muscles will be combining oxygen with glucose as fast as they can to make ATP which will provide the energy for the muscles A lot of energy is needed to work as hard as this One breathe deeper and faster to get more oxygen into the blood The heart beats faster to get the oxygen to the leg muscles as quickly as possible Eventually a limit is reached The heart and lungs cannot supply oxygen to the muscles any fater But more energy is still needed for the race How can that extra energy be found?
Extra Energy Production
Extra energy can be produced by anerobic respiration Some glucose is broken down without conbining it with oxygen Glucose + Lactic acid + energy This does not release very much energy but a little extra might make all the difference When the exercise stop there will still be quite a lot of lactic acid in the muscles and in the blood The lactic acid must be broken down by combining it with oxygen So even though the energy is not needed any more that still requires extra oxygen One has to continue breathing deeply and panting harder Extra oxygen is taken in to break down the lactic acid and combine it with oxygen Now as the lactic acid is combined with oxygen the debt is being paid off Until lactic acid is used up the breathing rate and rate of heart beat will return to normal
RQ Measurement
It is sometimes useful to be able to deduce which substrate is being used in a person’s metabolism at a specific time This can be done if the volume of oxygen taken in and the volume of carbon dioxide given out are measured From this data the respiratory quotient (RQ) can be calculated: $RQ=\frac{Volume~of~carbon~dioxide~given~off}{Volume~of~oxygen~taken~in}$
RQ Values
The RQ values of the following substrates are well documented from investigation
Carbohydrate RQ
1
Protein RQ
0.9
Fats/Oils RQ
0.7
RQ Data Interpretation
It is interesting to know which substrate is being metabolised It is necessary to view such data with caution If a mixture of substrates is being used them the figure will be different from the above e.g. an RQ of 0.8 could point to both protein and fat being used The graph below shows the different RQ values of a seed during different stages of germination
Seed Germination RQ
This graph suggests that the seed begins with carbohydrate as a metabolic changes to fat/oil then returns to mainly using carbohydrate Any RO which is not of the numbers given suggests a substrate combination is being used
Respirometer
The instrument called a respiroment is used to collect RQ data
Sodium Hydroxide Function
Sodium hydroxide absorbs all $Cl_{2}$ from the air in the apparatus from the beginning
Germinating Seeds in Respirometer
As the germinating seeds use oxygen and the pressure reduces in tube A so the manometer level nearest to the seed rises Any $C0{2}$ excreted is absorbed by the sodium hydroxide solution The syringe is used to return the manometer fluid levels to normal The volume of oxygen used is calculated by measuring the volume of gas needed from the syringe to return the levels to the original values N/B - Potassium hydroxide could be used instead of sodium hydroxide The both absorb $C0{2}$ - If water repalces the sodium hydroxide then the carbon dioxide evolved can be measured
Excretion Definition
Metabolic activities occur all the time in a cell Some of the by-products of such activities are poisonous and must be removed from the cell and eventually from the organism Sometimes a substance is present in excess amounts in a cell This too must be removed and got rid of if it cannot be stored The removal of such substances or wastes is known as excretion
Main Wastes
The main wastes are carbon dioxide and water formed as by-products during cellular respiration; oxygen in an actively photosynthesizing cell; nitrogenous wastes produced during the breakdown of excess amino acids; and excess water salts and other unnecessary substances that enter the cell during its metabolic activities
Waste Removal
Most wastes are present as an aqueous solution and are readily excreted through the cell membrane by diffusion or active transport In an aquatic protozoan like the Amoeba excess water enters the cell all the time by osmosis Such a cell usually gets rid of the excess water by means of a contractile vacuole (see page 336)
Cell Growth
A cell grows by increasing in mass and size (volume) The increase is due to the addition of more protoplasmic material When the cell reaches its maximum size it stops growing
Growth Process
Growth is an anabolic process For it to occur the cell needs plenty of food to provide the necessary energy and materials for building up new protoplasm
Unicellular Organism Growth
In a unicellular organism the young organism grows until it reaches its maximum size; then it reproduces to give rise to young individuals This usually happens by simple division of the adult cell into two daughter cells as in the Amoeba (fig 11-7)
Multicellular Organism Growth
All multicellular organisms begin life as a single fertilized cell This cell divides into two then into four and so on (fig 11-8) At the beginning the fertilized cell just divides to form smaller cells there is no increase in size Cell division is therefore the basis of growth in a multicellular organism It brings about an increase in the number of cells After cell division the daughter cells increase in mass and size i.e. enlarge Eventually each cell may develop into a special type of cell by changing its shape and structure to carry out a particular function (fig 11-9) The kind of cell it becomes depends on its position in the body of the organism In our body a cell may develop into a nerve cell if it is in the brain a muscle cell if it is in the heart or a ciliated lining cell if it is in the trachea This process is called cell differentiation and is important in the growth and development of a mature multicellular organism In a multicellular organism during the early stages of growth and development all the cells can divide These cells may also rearrange themselves so that they can enlarge and differentiate to give rise to the various parts of an organism in an orderly manner In a mature organism cell division is usually restricted to cells in certain regions of the body only This is because most specialized cells lose their ability to divide
Mitosis
The cell division that takes place during growth and development of an organism is known as mitosis It also occurs during asexual reproduction Mitosis takes place in somatic cells - body cells that are not involved in the production of gametes The somatic cell of a particular kind of organism has a characteristic number of chromosomes in its nucleus These chromosomes occur in pairs i.e. there are two sets of chromosomes The members of each pair are called homologous chromosomes For example each human somatic cell has 46 chromosomes These are present as 23 pairs of homologous chromosomes The number of chromosomes in each somatic cell of an organism is called the diploid number (2n)
Haploid Number
The number of chromosomes in each gamete is half the diploid number; it is called the haploid number (n)
Chromosome Number Maintenance
Thus when a sperm (n) fuses with an egg (n) during sexual reproduction the resulting fertilized egg has the diploid number of chromosomes (2n)
Mitosis Process
Mitosis is a continuous process but for convenience it is divided into four stages namely prophase metaphase anaphase and telophase (fig 11-10)
Prophase
During prophase the chromatin network in the nucleus condenses by coiling and folding to form short thick threads called chromosomes
Metaphase
During metaphase the chromosomes become arranged at the equator of the cell
Anaphase
During anaphase the centromere of each chromosome divides into two and the sister chromatids separate
Telophase
During telophase the sister chromatids reach the opposite poles of the cell and uncoil to form the chromatin network again
Cytokinesis
At the same time the cytoplasm divides to form two daughter cells
Mitosis Duration
The whole process of mitosis takes about 1-2 hours
Significance of Mitosis
Mitosis is important for the following reasons
Growth
It brings about growth in multicellular organisms by increasing the number of cells
Repair
It replaces worn-out cells
Asexual Reproduction
It is the method of reproduction in unicellular organisms like the Amoeba and the method of asexual reproduction in multicellular organisms like the Hydra and plants
Meiosis Definition
Meiosis is another type of cell division that occurs only in reproductive cells (sex cells or gametes) to produce more reproductive cells
Meiosis Product
It results in each daughter cell having half the number of chromosomes as the parent cell
Meiosis Process
Meiosis involves two successive divisions known as Meiosis I and Meiosis II
Meiosis I
In Meiosis I the homologous chromosomes separate
Meiosis II
In Meiosis II the sister chromatids separate
Meiosis I Stages
Meiosis I is divided into four stages namely prophase I metaphase I anaphase I and telophase I
Prophase I
Prophase I is similar to prophase in mitosis except that homologous chromosomes pair up in a process known as synapsis
Metaphase I
During metaphase I the homologous chromosomes are arranged at the equator of the cell
Anaphase I
During anaphase I the homologous chromosomes separate
Telophase I
During telophase I the homologous chromosomes reach the opposite poles of the cell
Meiosis II Stages
Meiosis II is similar to mitosis and is also divided into four stages namely prophase II metaphase II anaphase II and telophase II
Meiosis II Product
At the end of meiosis II four daughter cells are formed each of which has half the number of chromosomes as the parent cell
Meiosis Significance
Meiosis is important for the following reasons
Chromosome Number Maintenance
It ensures that the chromosome number remains constant from one generation to the next during sexual reproduction
Genetic Variation
It brings about genetic variation among organisms of the same species
