Cell Structure and Subcellular Components

Cell Structure

• Organelles are specialized subcellular structures within cells.
• Cells are the basic structural units of living organisms.
• Tissues are groups of cells with similar structures that work together.
• Organs are groups of tissues working together to perform specific functions.
• Organ systems consist of groups of organs with related functions that work together.
• An example is the respiratory organ system containing lungs (organ), made of epithelial tissue and epithelial cells.

Subcellular Structures in Plant and Animal Cells

• Nucleus: Contains genetic material (DNA) and codes for particular proteins, enclosed in a nuclear membrane.
• Cytoplasm: Liquid substance where chemical reactions occur, containing enzymes and organelles.
• Cell membrane: Contains receptor molecules to identify and selectively control what enters and leaves the cell.
• Mitochondria: Aerobic respiration occurs here providing energy for the cell
• Ribosomes: Functions in protein synthesis, found on the rough endoplasmic reticulum.
• Chloroplasts: Where photosynthesis occurs, providing food for the plant. Contains chlorophyll to harvest light for photosynthesis.
• Permanent vacuole: Contains cell sap, is found within the cytoplasm, and improves cells rigidity.
• Cell wall: Made from cellulose and provides strength to the cell.

Cell Differentiation and Specialization

• Specialized cells develop specific characteristics for particular functions.
• Cells specialize through differentiation, gaining new subcellular structures to suit their role.
• Cells can differentiate early or retain the ability to differentiate throughout life (stem cells).
• Most animal cells differentiate once, while plant cells often retain differentiation ability.

Examples of Specialized Cells in Animals

• Sperm Cells: Streamlined head and long tail aid swimming, many mitochondria supply energy for movement, and the acrosome has digestive enzymes to break down the egg membrane.
• Nerve Cells: Long axon for carrying impulses over distances, many dendrites for branched connections with other nerve cells, and nerve endings with many mitochondria that supply the energy to make special transmitter chemicals for passing neural impulses between cells.
• Muscle Cells: Specialized to contract quickly, containing special proteins (myosin and actin) that slide, many mitochondria for energy, and can store glycogen for respiration.

Examples of Specialized Cells in Plants

• Root Hair Cells: Specialized for water and mineral uptake through osmosis and active transport and have a large surface area due to root hairs for more water movement.
• Xylem Cells: Specialized to transport water and mineral ions, lignin makes the cells die and become hollow, forming continuous tubes for water and mineral movement.
• Phloem Cells: Cell walls form sieve plates, allowing the movement of substances from cell to cell. Loss of subcellular structures is offset by the mitochondria of companion cells providing energy for movement.

Stem Cells in Medicine

• A stem cell is an undifferentiated cell able to undergo mitosis to produce more cells.
• Some stem cells differentiate to have different functions.
• Stem cells are important in development, growth, and repair
• Embryonic stem cells can differentiate into any type of cell in the body
• Embryonic cells can be used to replace insulin cells in those suffering from diabetes or neural cells for those with Alzheimers
• Adult stem cells are usually found in bone marrow and form many types of cells including blood cells
• Meristems are found in root and shoot tips
• In plants, they can differentiate into any type of cells, and have this ability throughout the life of the plant

Stem Cells In Medicine Benefits/Risks

• Benefits: Replacement of damaged cells in conditions like type 1 diabetes, multiple sclerosis, and paralysis, bone marrow transplants for blood cell cancers, and potential for growing whole organs.
• Risks: Ethical concerns about destroying unused embryos, no guarantee of successful or safe therapies in the long term, possible mutations in cultured stem cells, and difficulty in finding suitable stem cell donors.

Biological Molecules

• Carbohydrates: Made of carbon, oxygen, and hydrogen, polymers broken down into simple sugars.
• Carbon, oxygen, hydrogen, sulfur, nitrogen, and phosphorus make proteins. Polymers that break down into its monomer: amino acids.
• Lipids (fats and oils): Made of carbon, oxygen, and hydrogen, broken down into 3 fatty acids and a glycerol.

Food Sample Tests

• Glucose Test: Solution turns brick red if glucose is present, stays blue if not.
• Starch Test: Solution turns blue-black if starch is present, remains brown if not.
• Protein Test: Solution turns purple if protein is present, stays blue if not
• Fat Test: Creates a milky white emulsion if fat is present; remains colorless if not.

Enzymes

• Biological catalysts that increase the rate of reaction without being used up. They are protein molecules.
• Active site where substrates bind is vital to the enzymes function
• Lock and Key Hypothesis: The shape of the substrate is complementary to the shape of the active site (enzyme specificity), so when they bind, it forms an enzyme-substrate complex.
• Once bound, the products are released from the surface of the enzyme
• Optimum is around 37°C (body temperature)
• The rate of reaction increases with an increase in temperature up to this optimum
• When the temperature becomes too hot, the bonds in the structure will break
• This changes the shape of the active site, so the substrate can no longer fit in
• The enzyme is said to be denatured and can no longer work

Practical: Investigate How Enzyme Activity Can Be Affected by Changes in Temperature

• Starch solution is heated to set temperature before amylase is added.
• Iodine is added to each well after a minute
• Measure the time it takes until the iodine stops turning blue-black starch broke down into glucose
• Repeat the test with different temperature
• If PH is too high or too low, the forces that hold the amino acid chains that make up the protein will be affected
• The enzyme is said to be denatured and can no longer work
• Amylase breaks down carbohydrates down into simple sugars, such as maltose
• Use iodine (dark orange color) to check for the presence of starch in the solution at any time

Practical: Investigate How Enzyme Activity Can Be Affected by Changes in pH

• Set pH in each test tube
• Add 2cm³ of amylase solution, 2cm³ of starch solution and 1cm³ of pH solution in a test tube and mix the solution
• Put this test tube into the water beaker and start a stopwatch. Temperature is a controlled variable
• Every 10 seconds, use a pipette to indicate that starch is
• Continue repeating until the solution and record the time taken
• Repeat Steps 1-6 with different pH solutions
• Record your results on a graph of pH and time taken to complete the reaction We can see what the optimum pH of amylase is, as it will be the pH where the reaction is

Movement in and out of cells

• Diffusion results in a net movement from an area of higher concentration to an area of lower concentration.
• Diffusion is a passive process, and no energy is required.
• The molecules have to be small, for example oxygen, glucose, amino acids, and water.
• Larger molecules, such as starch and proteins, cannot diffuse through the cell membrane.
• Single-celled organisms can use diffusion to transport molecules, and have a relatively large surface area to volume ratio.
• Multicellular organisms, the surface area to volume ratio is small so they cannot rely on diffusion alone. Instead, cell surfaces and organ systems have a number of adaptations that allow molecules to be transported in and out of cells.

Factors Affecting the Rate of Movement

• Concentration gradient: A greater difference increases the rate
• Temperature: Higher temperatures generally increase the rate.
• Surface area to volume ratio: A greater surface area increases the rate.
• Distance: A longer distance reduces the rate.

Osmosis

• Osmosis is the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane.
• A dilute solution of sugar has a high water potential, and a concentrated solution has a low water potential.
• The movement of water is passive, and it does not use energy.
• If external solutions concentration of sugar in cells is the same then no movement occurs
• If the concentration of sugar in external solution is higher than cells, water moves out
• If the concentration of sugar in external solution is lower water moves in.

Examples of Osmosis in Living Organisms

• Animal cells: More dilute causes burst and more concentrated causes shriveling
• For plant cells: Water moves into cell and then into vacuole
• If the external solution is more concentrated, water will move out of the cell and they will become soft. Eventually called plasmolysis the cell may die.
• Active transport is the movement of particles from an area of lower concentration to an area of higher concentration, i.e. against the concentration gradient.
• Substances such as glucose and amino acids have to move in the gut

Practical: Investigate Diffusion in Non-living Systems

• Cut cubes of sodium hydroxide and phenolphthalein indicator and add hydrochloric acid and measure

Photosynthesis

• It is an endothermic reaction in which light energy is converted into chemical energy within the chloroplasts.
• Carbon dioxide + water → glucose + oxygen or CO2 + H2O → O2 + C6H12O6

Factors affecting Photosynthesis

• As the reaction is controlled by enzymes, this trend only continues up to a certain temperature until the enzymes begin to denature and the rate of reaction decreases.
• For most plants, the higher the light intensity, the higher the rate of photosynthesis.
• As the concentration of carbon dioxide increases, the rate of reaction increases.

Practicals investigating Photosynthesis

• Use water plants, such as Elodea, which release bubbles of oxygen when photosynthesizing and a lamp with an LED bulb is set up beside.
• Sodium hydrogen carbonate (NaHCO3) is added to the water to supply carbon dioxide.
• For investigating the effect of light, place pondweed in water and set up a desk lamp next to a ruler so that you can measure the distance between the light and the beaker
• Repeat steps by moving the lamp away to investigate the effect of carbon dioxide or light on growth rate

Investigating starch reproduction

• Repeat the above experiment but with a variegated leaf. Variegated plants are white and green and only contain chlorophyll in the green part

Leaf Structures

• Waxy Cuticle: Helps to reduce water loss by evaporation and is a protective layer found at the top of the leaf
• Upper Epidermis: Very thin and transparent for light to enter the palisade mesophyll.
• Palisade Mesophyll: Contains lots of chloroplasts so that photosynthesis can happen rapidly
• Spongy Mesophyll: Allows gases to diffuse in and out of cells faster and increases surface area to value volume ratio
• Lower Epidermis: Contains guard cells and stomata (gaps).
• Guard Cell: Kidney-shaped cells that open and close the stomata by absorbing or losing water. When lots of water is available, the cells fill and openings
• Stomata: Gas exchange and loss of water by evaporation take place

Mineral Ions

• Mineral ions are chemicals necessary for life.
• Magnesium: Required for chlorophyll production
• Nitrate: Required to produce amino acids

Nutrition In Humans

• Humans need to eat a balanced diet consisting of carbohydrates, proteins, lipids, dietary fibre, vitamins, minerals, and water.
• Carbohydrates- A high energy source Bread, cereals, pasta, rice, potatoes
• Protein- Growth and repair Meat, fish, eggs, pulses
• Lipids- A high energy source and for insulation Butter, oil, nuts
• Vitamin A- Needed especially in the dark, and for growth Carrots, green vegetables
• Vitamin C- Helps to absorb iron Citrus fruits
• Vitamin D- Helps to absorb calcium Margarine, oily fish
• Dietary fibre-To provide roughage to keep food moving through gut - deficiency causes constipation Vegetables, bran
• Calcium- Deficiency leads to curving of bones Milk
• Iron- Deficiency could cause anaemia Red meat
• Water- Needed for cell reactions to take place Water, juice, milk

Factors Affecting Energy Requirements

• Age: Energy requirements increase as we approach adulthood and energy needs of adults go down as they age
• Activity levels: If you are more active, then you will need more energy for movement

Alimentary Canal

• Aids digestion for once food has been eaten
• Mouth; Mechanical digestion and chemical digestion
• Esophagus: Food bolus moves with peristalsis
• Pancreas: Secretes enzymes into the stomach and small intestine
• Gastric juice is made of pepsin and hydrochloric acid
• Small intestine is made up of carbohydrates Bile is produced in the liver , neutralises hydrochloric acid
• Bile breaks drops of fat

Human Alimentary Canal - Ileum

• Lined with villi (finger-like projections) to maximise absorption of digested soluble molecules into blood
• Villi thin lining, large network of capillaries and have a large surface area

Digestive enzymes

• Broken down carbohydrates and proteases to amino acids lipids to fatty acids

Large Intestine

• Water is absorbed here, to produce feces and stores in the rectum

Practical: Investigate the Energy Content in a Food Sample

• Measured by calorimetry , pour cold water into a tube
• Record the starting temperature of the water with a thermometer
• Heat can burn the thermometer if too high and the specific capcity will be at 1 degree

Aerobic Respiration

• Aerobic respiration uses oxygen, yields to most energy and most reactions occur in the mitochondria.
• Anaerobic doesn't yield to much energy and is a reaction for sprints

Practical on Respiration

• To find where indicator has yellow (high concentration)
• Living germinating seeds are needed to increase

Gas exchange

• In order for plants to photosynthesise and respire, gas exchange of oxygen and carbon dioxide
• Adaptations of leaves for gas exchange have many of these adaptations have been mentioned
• Spongy mesophyll increases increases the surface area to volume ratio
• Flattened shape increases surface area for absorption of light and carbon dioxide

Respiration At Night

• Respiration occurs during night and day, as plants require energy at all times
• The closer the lamp is to the plant, the stronger the light intensity and therefore the rate of photosynthesis increases, for photosynthesis increases. This means that there is more carbon dioxide taken in by the plant

Respiratory System In Humans

• Ribs: Bone around the lungs to provide protection of internal organs
• Intercostal muscle: Muscles that control inhalation and exhalation
• Muscular dome at the bottom of thorax
• Diaphragm: Creates pressure to control inhalation of exhalation
• Trachea: The windpipe where air enters
• Bronchi: Trachaea divides into 2
• Bronchioles Small connected to the alveoli
• Lumen - Allows the blood walls to connect and have exchange

Alveoli And Transport

• Diffusion of cells
• High to low Intercostal muscles contract •Ribcage moves up and out •Diaphragm contracts downwards •Pressure decreases •Air moves in

Adaptations For transport In Plants

• Phloem transports sucrose and amino acids, has elongated cells.
• Xylem - Water travels up the xylem from the roots and Lignin creates hollow areas for this

Transpiration

• Evaporation of water
• Plants absorb water from soil because these water cells join together

Factors That Effect Transpiration

• Environmental factors determine the rate

Transport In Humans

• Important in the transfer of carbon

White Blood Cells

• Part of immune system to fight and they neutralise toxins

Platelets

• Have a broken skin to cause a reaction and have a series of reactions

Vaccination

• To build ammune against desiesed or certain illnesses
• If memory cells produce quicker at a certain range

Human Circulatory System

• Transports throughout body
• If lungs increase, it can pump water and pump blood around the body

Heart

• Pumps better and stroke volume also includes
• Volume of heart will pump faster

Homeostasis

• Three things needed a stimulus a receptor and effector
• Plants use light energy to transport or geotropic to gravity

Explore the fundamental structure of cells, the basic units of life, and their organization into tissues, organs, and organ systems. Learn about key subcellular structures in both plant and animal cells, including the nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes, each with specialized functions.