Cell Structure and Organelles

Cell Biology

Cell Structure

• Plasma membrane: semi-permeable membrane that surrounds the cell
• Cytoplasm: jelly-like substance inside the cell where metabolic reactions occur
• Nucleus: contains most of the cell's genetic material (DNA)
• Mitochondria: generates energy for the cell through cellular respiration
• Endoplasmic reticulum (ER): network of membranous tubules and cisternae involved in protein synthesis and transport
• Ribosomes: site of protein synthesis
• Lysosomes: contain digestive enzymes that break down and recycle cellular waste and foreign substances

Cell Function

• Cellular respiration: process of generating energy for the cell through the breakdown of glucose
• Photosynthesis: process of generating energy for the cell through the conversion of light energy
• Cell signaling: process of communication between cells through signaling molecules
• Cell division: process of cell growth and reproduction, including mitosis and meiosis

Nutrition

Nutrients

• Carbohydrates: provide energy for the body, examples include sugars, starches, and fibers
• Proteins: build and repair tissues, examples include amino acids
• Fats: provide energy and insulation, examples include triglycerides and phospholipids
• Vitamins: essential nutrients that cannot be synthesized by the body, examples include vitamin C and vitamin D
• Minerals: essential nutrients that cannot be synthesized by the body, examples include calcium and iron

Nutritional Processes

• Ingestion: process of taking in food through the mouth
• Digestion: process of breaking down food into smaller molecules that can be absorbed by the body
• Absorption: process of taking in nutrients through the walls of the digestive tract
• Assimilation: process of using absorbed nutrients for energy, growth, and repair
• Elimination: process of removing waste products from the body

Cell Biology

Cell Structure

• The plasma membrane is a semi-permeable membrane that surrounds the cell, regulating what enters and leaves.
• Cytoplasm is a jelly-like substance inside the cell where metabolic reactions occur, maintaining cellular shape and providing mechanical support.
• The nucleus contains most of the cell's genetic material (DNA), which is organized into linear chromosomes.
• Mitochondria are the site of cellular respiration, generating energy for the cell through the breakdown of glucose and other organic molecules.
• The endoplasmic reticulum (ER) is a network of membranous tubules and cisternae involved in protein synthesis, transport, and lipid synthesis.
• Ribosomes are the site of protein synthesis, reading messenger RNA (mRNA) to assemble amino acids into polypeptide chains.
• Lysosomes contain digestive enzymes that break down and recycle cellular waste and foreign substances, maintaining cellular homeostasis.

Cell Function

• Cellular respiration is the process of generating energy for the cell through the breakdown of glucose, involving glycolysis, pyruvate oxidation, and the electron transport chain.
• Photosynthesis is the process of generating energy for the cell through the conversion of light energy, involving the absorption of light by pigments and the production of ATP and NADPH.
• Cell signaling is the process of communication between cells through signaling molecules, such as hormones and neurotransmitters, which bind to receptors to initiate responses.
• Cell division involves the reproduction of cells through mitosis (for somatic cells) and meiosis (for gametes), ensuring genetic continuity and diversity.

Nutrition

Nutrients

• Carbohydrates are energy-rich molecules that provide fuel for the body, with examples including sugars (e.g., glucose), starches (e.g., amylose), and fibers (e.g., cellulose).
• Proteins are complex biomolecules that build and repair tissues, composed of amino acids linked by peptide bonds.
• Fats are energy-dense molecules that provide insulation and energy, with examples including triglycerides (e.g., triolein) and phospholipids (e.g., lecithin).
• Vitamins are essential nutrients that cannot be synthesized by the body, with examples including vitamin C (ascorbic acid) and vitamin D (cholecalciferol).
• Minerals are essential nutrients that cannot be synthesized by the body, with examples including calcium (Ca) and iron (Fe), which are crucial for bone health and oxygen transport.

Nutritional Processes

• Ingestion involves the mechanical breakdown of food through chewing and the chemical breakdown of food through saliva and gastric juices.
• Digestion involves the enzymatic breakdown of macromolecules into smaller molecules, such as amino acids, sugars, and fatty acids.
• Absorption involves the uptake of nutrients through the walls of the digestive tract into the bloodstream, where they can be distributed to cells.
• Assimilation involves the use of absorbed nutrients for energy, growth, and repair, with excess energy stored as glycogen or fat.
• Elimination involves the removal of waste products, such as urea, carbon dioxide, and feces, through excretory organs like the kidneys and liver.

Life Processes

• Life processes are the maintenance functions of living organisms that need to go on even when they are not doing anything particular.
• These processes are needed to prevent damage and break-down, and energy is needed for them, which comes from outside the body of the individual organism.

What are Life Processes?

• Life processes include:
  • Nutrition: the process of obtaining energy and materials from outside the body.
  • Respiration: the process of using oxygen to break-down food sources for cellular needs.
  • Transportation: the process of carrying food and oxygen from one place to another in the body.
  • Excretion: the process of removing waste by-products from the body.

Nutrition

• Nutrition is the process of obtaining energy and materials from outside the body.
• Autotrophic nutrition: the process by which autotrophs (e.g. green plants and some bacteria) convert carbon dioxide and water into stored forms of energy using sunlight and chlorophyll.
• Heterotrophic nutrition: the process by which heterotrophs (e.g. animals and fungi) obtain energy and materials from other organisms.

Autotrophic Nutrition

• Autotrophic nutrition involves photosynthesis, which is the process by which autotrophs convert carbon dioxide and water into stored forms of energy using sunlight and chlorophyll.
• Photosynthesis involves:
  • Absorption of light energy by chlorophyll.
  • Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
  • Reduction of carbon dioxide to carbohydrates.

Heterotrophic Nutrition

• Heterotrophic nutrition involves obtaining energy and materials from other organisms.
• Examples of heterotrophic nutrition include:
  • Fungi breaking down food material outside the body and absorbing it.
  • Animals taking in whole material and breaking it down inside their bodies.
  • Parasites deriving nutrition from plants or animals without killing them.

How do Organisms obtain their Nutrition?

• Different organisms have specialized digestive systems depending on their body design and functioning.
• In single-celled organisms, the food is taken in by the entire surface.
• In complex organisms, different parts become specialized to perform different functions.

Nutrition in Human Beings

• The alimentary canal is a long tube extending from the mouth to the anus.
• The alimentary canal has different parts that are specialized to perform different functions.
• Digestion of food occurs in the alimentary canal, with the help of enzymes such as salivary amylase.

Importance of Chlorophyll and Light Energy in Photosynthesis

• Chlorophyll is essential for photosynthesis, as it absorbs light energy and converts it to chemical energy.
• Light energy is necessary for photosynthesis, and chlorophyll is the key component that makes this process possible.### Digestion and Absorption of Food
• The alimentary canal is a long tube that extends from the mouth to the anus.
• The lining of the canal is soft and wet to facilitate the passage of food.
• Saliva secreted by the salivary glands contains an enzyme called salivary amylase that breaks down starch into sugar.
• The food is mixed thoroughly with saliva and moved around the mouth while chewing by the muscular tongue.
• The lining of the canal has muscles that contract rhythmically to push the food forward through peristaltic movements.
• The stomach is a large organ that expands when food enters it, and the muscular walls of the stomach mix the food thoroughly with more digestive juices.
• The digestive juices in the stomach are produced by gastric glands and contain hydrochloric acid and pepsin.
• The hydrochloric acid creates an acidic medium that facilitates the action of the enzyme pepsin.
• The mucus protects the inner lining of the stomach from the action of the acid.

Small Intestine

• The small intestine is the longest part of the alimentary canal and is fitted into a compact space due to extensive coiling.
• The length of the small intestine differs in various animals depending on the food they eat.
• Herbivores have a longer small intestine to allow cellulose to be digested, while carnivores have a shorter small intestine since meat is easier to digest.
• The small intestine is the site of the complete digestion of carbohydrates, proteins, and fats.
• The small intestine receives secretions from the liver and pancreas for digestion.
• Bile juice from the liver makes the food alkaline, allowing pancreatic enzymes to act.
• Pancreatic juice contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats.

Absorption of Digested Food

• The walls of the small intestine contain glands that secrete intestinal juice.
• Enzymes in the intestinal juice finally convert proteins to amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
• The digested food is taken up by the walls of the intestine.
• The inner lining of the small intestine has numerous finger-like projections called villi that increase the surface area for absorption.
• The villi are richly supplied with blood vessels that take the absorbed food to each and every cell of the body.

Respiratory System

• The energy released during cellular respiration is used to synthesise ATP, which is used to fuel all other activities in the cell.
• ATP is the energy currency for most cellular processes.
• The energy released during respiration is used to make an ATP molecule from ADP and inorganic phosphate.
• Endothermic processes in the cell use this ATP to drive the reactions.

Transportation in Human Beings

• Blood is a fluid connective tissue that transports food, oxygen, and waste materials in our bodies.

• Plasma transports food, carbon dioxide, and nitrogenous wastes in dissolved form.

• Oxygen is carried by the red blood cells.

• Many other substances like salts are also transported by the blood.### The Heart and Blood Vessels

• The heart is a muscular organ that pumps blood throughout the body.

• It has four chambers: the left and right atria, and the left and right ventricles.

• The left and right sides of the heart are separated to prevent oxygenated and deoxygenated blood from mixing.

• The heart pumps oxygen-rich blood from the lungs to the body and deoxygenated blood from the body to the lungs.

Blood Pressure

• Blood pressure is the force of blood against the walls of blood vessels.
• It is measured in mm of Hg (millimeters of mercury).
• Normal blood pressure is around 120/80 mm Hg.
• High blood pressure (hypertension) can lead to the rupture of an artery and internal bleeding.

Blood Vessels

• Arteries carry blood away from the heart to organs and tissues.
• They have thick, elastic walls to withstand high blood pressure.
• Veins collect blood from organs and tissues and bring it back to the heart.
• They have valves to prevent blood from flowing backward.
• Capillaries are the smallest blood vessels, where oxygen and nutrients are exchanged with cells.

Platelets and Blood Clotting

• Platelets are blood cells that help to plug leaks in blood vessels and form blood clots.
• They circulate in the blood and respond to injuries by aggregating and forming a platelet plug.
• Blood clotting is a crucial process that prevents excessive blood loss in case of injury.

Lymphatic System

• The lymphatic system is a network of vessels, organs, and tissues that help to defend the body against infection and disease.
• It absorbs and transports fats and fat-soluble vitamins from the digestive system.
• Lymphatic vessels drain excess fluid from tissues and return it to the bloodstream.

Transportation in Plants

• Plants have a transportation system that moves water, minerals, and nutrients from the roots to the leaves and other parts of the plant.
• The xylem transports water and minerals from the roots to the leaves, while the phloem transports sugars and other organic compounds from the leaves to other parts of the plant.
• The process of transpiration creates a suction force that pulls water up the xylem.
• Xylem and phloem tissues are organized into vascular bundles that run throughout the plant.

Excretion in Human Beings

• The excretory system in human beings consists of the kidneys, ureters, urinary bladder, and urethra.
• The kidneys filter waste products from the blood and produce urine.
• Urine passes through the ureters to the urinary bladder, where it is stored until it is released through the urethra.
• The kidneys also regulate electrolyte levels and maintain acid-base balance in the body.

Artificial Kidney (Hemodialysis)

• Artificial kidney (hemodialysis) is a treatment for kidney failure, where a machine takes over the function of the kidneys to remove waste products from the blood.