Animal and Plant Cells

Cell Structure

• All living things consist of cells, either prokaryotic or eukaryotic.
• Animal and plant cells are eukaryotic.
• Eukaryotic cells have a cell membrane, cytoplasm and a nucleus containing DNA.
• Bacterial cells are prokaryotic and much smaller.
• Prokaryotic cells have a cell wall, cell membrane, cytoplasm, a single circular strand of DNA and plasmids.
• Organelles refer to structures in a cell that have different functions (e.g. cell membrane).
• Cells are extremely small, so orders of magnitude can be used to understand their relative sizes.
• Prefixes placed before units of measurement (e.g., meters) indicate the multiple of the unit.
  • Centi multiplies the unit by 0.01.
  • Milli multiplies the unit by 0.001.
  • Micro multiplies the unit by 0.000,001.
  • Nano multiplies the unit by 0.000,000,001

Animal and Plant Cells

• Subcellular structures inside cells have specific functions.
• Nucleus contains DNA to build new cells and is enclosed in a nuclear membrane.
• Cytoplasm is a liquid substance where chemical reactions occur.
  • Cytoplasm contains enzymes to speed up reactions.
  • Cytoplasm houses organelles.
• Cell membrane regulates what enters and leaves the cell.
• Mitochondria are where aerobic respiration occurs, providing energy.
• Ribosomes are where protein synthesis occurs, located on the rough endoplasmic reticulum.
• Chloroplasts are where photosynthesis occurs, providing food for the plant and contains chlorophyll for harvesting light.
• Permanent vacuole contains cell sap and improves cell rigidity, located within the cytoplasm.
• Cell wall, present in algal cells, is made of cellulose and provides strength to the cell.
• Bacterial cells, being prokaryotic, lack the organelle diversity of animal and plant cells.

Bacterial Cells

• Cytoplasm present
• Cell membrane present
• Cell wall made of peptidoglycan.
• Single circular strand of DNA floats in the cytoplasm.
• Plasmids are small rings of DNA.

Cell Specialization

• Cells undergo differentiation, gaining new subcellular structures to suit their role.
• Cells either differentiate early on or have lifelong ability to differentiate like stem cells.
• In animals, most cells differentiate once, while plant cells often retain the ability.
• Sperm cells are streamlined with a long tail for swimming to egg
  • They contain many mitochondria to supply the energy to move
  • The acrosome at the head has digestive enzymes to break down the egg's membrane.
• Nerve cells transmit electrical signals from one place to another.
  • The axon is long, enabling the impulses to be carried along long distances
  • They have extensions (dendrites) to form branched connections with other nerve cells
  • The nerve endings have many mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters, to allow the impulse to be passed from one cell to another.
• Muscle cells:
  • Muscle cells can contract quickly (striated muscle) to move bones
  • Muscle cells can squeeze (smooth muscle like those in blood vessels) to vary blood pressure.
  • Special proteins (myosin and actin) slide over each other to contract the muscle.
  • Many mitochondria provide energy from respiration for contraction
  • They store the chemical, glycogen.
• Root hair cells take up water by osmosis and mineral ions via active transport.
  • They have a large surface area due to root hairs, allowing more water movement
  • Their large permanent vacuole affects the movement of water from the soil to the cell
  • The mitochondria provides energy from respiration
• Xylem cells transport water and mineral ions up the plant.
  • During formation, lignin deposition causes cell death to form a hollow, continuous tube
  • Lignin deposits in spirals helping the cells withstand pressure from water movement
• Phloem cells carry photosynthesis products (food)
  • Cell walls form sieve plates, to allow movement of substances.
  • Despite losing some subcellular structures energy is supplied by the mitochondria of the companion cells.

Cell Differentiation

• Stem cells undergo differentiation to become specialized by activating or deactivating certain genes to produce different proteins.
• In animals, most cells differentiate early and lose the ability except adult stem cells.
• Most specialized cells replicate through mitosis, but some (like red blood cells) are replaced by adult stem cells due to nucleus loss.
• In mature animals, cell division is mostly for repair or replacement of damaged cells.
• In plants, cells can differentiate throughout life at their final position.

Microscopy

• Microscopes enlarge extremely small structures.
• Robert Hooke observed the first cells in 1665 using a light microscope.
• Light microscopes have an objective and eyepiece lens
  • The objective lens produces a magnified image, which is then magnified and directed into the eye by the eyepiece lens
  • Light microscopes are usually illuminated from underneath
  • Light microscopes feature a maximum magnification of x2000 and a 200nm resolving power.
  • Light microscopes are used to view tissues, cells and large subcellular structures
• In the 1930s the electron microscope was developed, enabling scientists to view deep inside sub-cellular structures, such as mitochondria, ribosomes, chloroplasts and plasmids.
• Electron microscopes use electrons to form images due to their smaller wavelength.
  • There are scanning electron microscopes, that create 3D images, and transmission electron microscopes for detailed 2D organelle images.
  • Electron microscopes feature a magnification of up to x2,000,000 and respectively 10nm (SEM) and 0.2nm (TEM) resolving power
• Magnification of a light microscope: magnification of the eyepiece lens x magnification of the objective lens
• Size of an object: size of image/magnification = size of object

Culturing Microorganisms

• Microorganisms are cultured to study them in the lab.
• The culture medium contains carbohydrates, minerals, proteins and vitamins.
• Microorganisms are cultured in nutrient broth solutions or on agar gel plates.
• Nutrient both solution involves mixing bacteria with sterile nutrient broth in a flask, sealed with cotton wool
• An agar gel plate involves bacteria forming colonies on the agar surface.
• To make a plate: Poured into a sterilised petri dish, wire loops called inoculating loops dipped in bacteria and spread over the agar and sealed with a lid and incubated upside down.
• Petri dishes and culture media must be sterilized before use, commonly with an autoclave or UV light
  • Otherwise, contamination with other microorganisms may occur, potentially leading to harmful mutations.
• Inoculating loops must be sterilized by passing them through a flame.
  • This process kills unwanted microorganisms.
• The Petri dish lid should be sealed (but not completely) with tape.
  • This prevents airborne microorganisms from entering and forming deadly anaerobic bacteria as a result of a lack of oxygen.
• The Petri dish should be stored upside down.
  • This prevents the lid condensation from disrupting the agar surface and growth.
• The culture should be incubated at 25 degrees.
  • This prevents the growing of possible dangerous bacteria at higher temperatures such as 37c, instead colonies of bacteria are not able to grow at low temperatures
• Bacteria multiply by binary fission.
• Bacterial populations can be calculated using: bacteria at beginning x 2number of divisions = bacteria at end
• The number of divisions can be found by dividing the time the population is left for by the bacteria's mean division time
• Test the effects of antibiotics/disinfectants involves soaking paper discs in various antibiotics and placing them on a bacterial agar plate.
• Effective antibiotics are indicated from the size of the clear area around the paper
  • A control disc containing sterile water should be used, showing no death of bacteria with only the form of antibiotic affecting the zone of inhibition
• Antibiotic resistance is indicated when the antibiotic-resistant bacteria will not die and leave no inhibition zone

Cell Division

• Chromosomes, containing coils of DNA, contain genetic information.
• A gene is a DNA section coding for a protein that controls a characteristic.
• Chromosomes come in 23 pairs in each cell
• Sex cells (gametes) contain half, i.e. 23 chromosomes in each cell
• The cell cycle is a series of steps a cells has to undertake to divide.
• Mitosis is a step during this cycle, where a cell divides

Mitosis

• Interphase: The cell grows, organelles increase, synthesis of proteins occurs, DNA is replicated and energy stores are increased
• Mitosis: The chromosomes line-up at the cell equator and cell fibres pull chromosomes of the 'X' to opposite sides.
• Cytokinesis: The cytoplasm and cell membranes divide for two identical daughter cells
• Mitosis is important for development, growth and when replacing damaged cells in multicellular organisms
• It is a vital stage for asexual reproduction, simply replicating its own cells to produce offspring

Stem Cells

• Stem cells are undifferentiated cells that divide to produce more cells, which differentiate to perform functions.
• Embryonic stem cells:
  • Are formed when egg and sperm cells fuse to form a zygote
  • Can differentiate into any type of cell in the body
  • Can be cloned and directed the differentiate into almost any cell in the body
  • Could potentially replace insulin or nerve cells
• Adult stem cells:
  • Found in bone marrow and can form many types of cells
• Meristems in plants:
  • Found in root and shoot tips and exist throughout the plant’s lifespan
  • Can be used to clone plants with disease resistance and save rare plants
• Therapeutic cloning involves producing an embryo with the same genes as the patient.
  • Can be grown into any cell the patient needs
  • Advantage is that it would not be rejected
• Benefits v problems of research with stem cells:
  • Stem sell research can be used to replace diseased or damaged parts, and unwanted embryos could otherwise be used
  • Process of differentiation is incompletely understand so its hard to control stem cells

Transport In Cells

• The definition of diffusion = 'the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
• Many particles collide resulting in them moving and mixing, with no energy required
• Substances move via diffusion through cell membranes
  • Small molecules can move through such as oxygen, glucose, and water, but not proteins and starch
• Oxygen diffuses though the membranes of the alveoli into red blood cells for respiration.
• Carbon dioxide moves from red blood cells into the lungs to be exhaled.
• Diffusion of gases is called gas exchange
• Urea from liver cells moves into the blood plasma to be transported to the kidneys

Effect of Rate of diffusion

• The greater the difference in concentration will cause faster rate of diffusion
• The greater the temperature the greater rate of diffusion will be
• Greater the surface area of the membrane will enable the faster rate of diffusion
• Surface area to volume ratio relates to the size of the surface are of the organism relating to its volume,
  • which is calculated by finding volume and surface are, then writing in smallest whole numbers.
• If this is large, the organism is less likely to require specialised exchange surfaces and a transport system because the rate of diffusion is sufficient in supplying and removing the necessary gases
  • A larger SA:V enables the faster gas exchange in supplying needed elements
• Oxygen, water and carbon dioxide are transported into single-celled organisms due to a large SA:V ratio, which fulfil low metabolic needs.
• Multicellular have adapted surfaces and organ systems due to smaller volume and low SA:V ratios

Examples of adaptations

• The lungs transfer oxygen to the blood and carbon dioxide (gas exchange) takes place across millions of alveoli sacs which capillaries cover.
• Digested food is absorbed over the membranes in cells of the villi and in the bloodstream
• Gas exchange via diffusion takes place in the gills of a fish, and into/out of water. - Each gill has plates of gill filaments which contain lamellae, and enable oxygen diffusion to occur
• Plant roots also have root hair cells which increase surface area which also projects into the soil. - Roots enable uptake of water and mineral ions

Osmosis

• Osmosis: which is the movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane - A dilute sugar solution had a high water concentration.
• A concentrated solution has low concentration of water - Water moves from a dilute to concentrated area, moving from higher to lower water potential and in response to the concentration gradient
• Cytoplasm contains salts and sugars which causes movement of water to occur when water is in solution in the cell
• Plants do better in water compared to external solutions of sugar: - If outside, it enters cells to create turgor which is the ability to keep leaves rigid - If not in distilled water, the water moves cells out and become soft, cell membrane moves from cell wall and death occurs
• Model partially permeable membrane bad with sugar in a tube to see concentrations of the water inside and outside - Isotonic is no movement compared to cells - Hypertonic is water moves out - Hypotonic is water moves in

Osmosis In Animals

• In animals: - More dilute is water bursts, more concentrated is shrivelling

Active Transport

• The placement the sugar solutions results in varying tubers.
• Tubers measured for the tuber results in varying size, dependent upon the solutions.
• To see conc of internal of external solution, this helps show lightness
• The original change effects mass, plotting on change with graphs.
• Active transport occurs through different areas, with an area in a lower to higher concentration

Locations of Active Transport

• In roots hair: - They take mineral ions from soil, with mineral ions usually in higher concentrations in cells, meaning diffusion can not take effect from low to high concentrations. This requires respiration of energy.
• In gut: - Glucose and amino acids require transport into the bloodstream, and sugar molecules require active transport to move sugar in the blood from the gut - This helps for diffusion.