Life Processes

Nucleus :

·                The nucleus controls the activities (chemical reactions) carried out by the cell by making enzymes in the DNA of the nucleus. Enzymes diffuse to the cytoplasm of the cell.

·                It contains genetic material in DNA making up the chromosomes and the genes that code for the production of specific proteins.

·                It produces mRNA to produce structural proteins, like collagen and functional proteins, like, enzymes.

·                It initiates cell division.

Cytoplasm :

·                It contains cell organelles, like mitochondria.

·                It is the site of chemical reactions, like those of respiration and protein synthesis.

·                It stores substances, as glycogen.

·                It plays a skeletal role in supporting the cell.

·                It handles materials going in and out of cells.

It is complex in composition, but is largely made of water.

Cell Membrane :

·                It surrounds the cell.

·                It is partially permeable.

·                It exerts control over movement of substances in and out of the cytoplasm of the cell by diffusion, osmosis and active transport.

·                It forms vesicles during phagocytosis.

·                It keeps wanted materials in the cell.

Mitochondria :

·                Mitochondria contains enzymes in their folded inner membrane, called cristae.

·                Cristae increase surface area for enzyme activity.

·                Enzymes bring about aerobic respiration.

·                Glucose and oxygen react when enzymes act upon them.

·                Energy is released and ATP is formed.

·                Energy is used to drive metabolic processes / muscle contraction / active transport.

·                Examples of process that require energy are mitosis and protein synthesis.

Ribosomes :

·                They interpret the code in / decode the mRNA. This is called translation.

·                Ribosomes attract tRNA, bringing amino acids with them and collecting the amino acids.

·                They arrange amino acids according to the order of the DNA code.

·                They join amino acids with peptide bonds to form proteins.

ENZYMES :

Definition :

·                Enzymes are proteins, that act as biological catalysts.

·                They speed up chemical reactions.

·                They remain unchanged at the end of the reaction.

·                Some enzymes are intracellular, some are extracellular.

Function / Usefulness : Many reactions occur in body cells, that would occur too slowly if there are no enzymes and would require too high a temperature to react without enzymes. Too little synthesis of materials would then occur.

Structure :

·                Enzymes are proteins in nature, made of chains of amino acids, linked by peptide bonds.

·                Protein molecules consist of carbon, hydrogen, oxygen and nitrogen and are polymers.

·                They have a specific shape and an active site where the substrate fits in, like a lock into a key.

Function : They act as catalysts by lower activation energy to increase the rate of the reaction, and it remains unchanged.

Effect of temperature on enzyme activity :

·                Increased temperature leads to increased rate of reaction.

·                Enzymes are more active at higher temperatures as both substrate and enzyme molecules have more kinetic energy.

·                Frequency of collisions between the active site and substrate molecules increases and the collisions are harder.

·                Rate doubles for a rise in 10°C, upto 35 – 40°C.

·                Each enzyme has an optimum temperature.

·                At very high temperatures, enzymes are denatured as increased kinetic energy, leads to increased molecular vibrations.

·                The hydrogen bonds are broken, which causes the enzyme to lose its shape.

·                The shape of its active site is also changed, so that the substrate molecules no longer fit into it.

·                The catalytic activity of enzymes is lost. So, they become inactive.

·                Chemical reactions slow down or may even stop.

Effect of pH on enzyme activity :

·                Each enzyme has an optimum pH, such as, pepsin works best at pH 2.

·                Wrong pH changes the shape of the enzyme molecule by affecting the active site.

·                Enzymes are inactive if they are outside the narrow pH range they work best in.

·                If pH is restored, they become active again.

Experiment to show enzyme activity at different temperatures :

·                Control : Water baths at different temperatures

·                Organism : Amylase digests starch to maltose (reducing sugar)

·                Repeat : Samples are taken at each temperature

·                Measure : Iodine solution to show presence of starch. Benedict’s test for sugars. Comparison of time for reaction to occur. Determine end point.

·                Same : Volume of starch and enzymes to ensure a fair test

Experiment to show starch digestion :

·                Control : Starch is mixed with water and is kept in a water bath at suitable temperature

·                Organism : Amylase is added. Amylase digests starch to maltose (reducing sugar)

·                Repeat :

·                Measure : Take samples and test with iodine solution. If a blue – black colouration is seen, starch is still present. It turns brown / orange when all starch is gone. Test the remainder with Benedict’s solution. It turns red showing sugar is present.

·                Same :

Tissue : A collection of large number of cells, usually of similar structure, working together to carry out a specific function is called a tissue. For example,

·                Muscle consists of many fibres. All can contract to bring about movement, as in, the biceps muscle can cause movement of limb at the joint.

·                Epithelium

Aerobic respiration :

·                Oxygen and glucose react under the influence of enzymes present in the cristae / inner membrane of the mitochondria.

·                Energy from glucose is released.

·                A lot of energy is released, thus a lot of ATP is made.

·                Carbon dioxide and water are waste products.

·                ATP is made by using energy to combine ADP and phosphate group.

·                ATP is stored in the cell.

·                When energy is required, ATP breaks down.

Anaerobic respiration :

·                This supplies the additional energy needed. (A cell may be very active and aerobic respiration may not provide enough oxygen for aerobic respiration and not release enough energy.

·                This occurs in absence of oxygen.

·                Glucose is partially broken down and the end product is lactic acid.

·                This causes oxygen debt as lactic acid accumulates in the muscle cells.

·                Lactic acid is toxic and can cause pain and muscle cramps.

·                This can cause muscle fatigue.

·                It is broken down into water and carbon dioxide for excretion in the presence of oxygen.

·                A small amount of energy is released by anaerobic respiration.

·                Lactic acid is converted to glycogen in the liver.

Disadvantages of Anaerobic Respiration:

·                Minimal amount of lactic acid is tolerated by body cells as it is toxic and causes cramps

·                It is a wasteful use of energy reserves.

Differences between Aerobic and Anaerobic Respiration:

Aerobic	Anaerobic
End product is lactic acid	End products are carbon dioxide and water
Requires oxygen	No oxygen is needed
Glucose molecule is completely broken down, so a large number of ATP molecules are formed. A lot of energy is released	Glucose molecule is partially broken down. A few ATP molecules are made. Little energy is released
Occurs in mitochondria	Occurs in cell cytoplasm
No payment of oxygen debt	Repay oxygen debt

Protein Synthesis :

·                DNA in nucleus codes for the production of proteins.

·                DNA unzips by the use of enzymes to form corresponding mRNA. This is called transcription.

·                Nucleotides position according to the DNA code. Every 3 nucleotides / bases codes for 1 amino acid.

·                mRNA pass out of the nucleus through pores in the nuclear membrane to the ribosomes in the endoplasmic reticulum, found in the cytoplasm.

·                The ribosomes decode the mRNA. This is called translation.

·                Sequence of bases / codons on RNA determines the order of the amino acids.

·                The correct amino acids are attracted, collected as tRNA attaches to specific amino acid.

·                The amino acids arrive at the ribosomes via endoplasmic reticulum.

·                The amino acids in the correct order are arranged in a chain, linked by peptide bonds to form a polypeptide.

·                Thus a protein is made.

·                Protein synthesis requires energy from ATP, that is released by mitochondria.

·                The amino acids in the cytoplasm come from the person’s diet.

Proteins affect metabolic activity of cells. Some of the proteins formed are used to make enzymes that control chemical reactions in cells by speeding up metabolism.

Differences between Squamous Epithelium and Ciliated Epithelium :

SQUAMOUS	CILIATED
Flattened / lens shaped	Columnar in shape with cilia on free edge that beat to move mucus / ova
Forms continuous layer	Does not form continuous layer
Found in lining of mouth, gut, blood vessels, lungs, heart, skin	Found in linings of airways, trachea, bronchi, oviduct

Differences between Epithelial Cells and Red Blood Cells :

EPITHELIAL CELLS	RED BLOOD CELLS
Has a nucleus	Has no nucleus
Has no regular, biconcave shape	Has a regular, biconcave shape

Diffusion : Diffusion is the random movement of particles / ions from a region of high concentration to a region of low concentration, that is, down concentration gradient.