Cytology Honor

Nature Study

Requirements

1. What are the 3 parts of a eukaryotic cell? Name some of their functions.

   Answer: Plasma membrane (protection/exchange), cytoplasm (organelles/metabolism), and nucleus (DNA/control). Eukaryote = a defined nucleus with a nuclear membrane. — The eukaryotic cell is universal in animals, plants, fungi, and protists. The membrane is a selective lipid bilayer. The cytoplasm contains organelles (mitochondria, reticulum, ribosomes). The nucleus stores the genetic material separated by a double membrane. The difference from prokaryotes: these do not have a defined nucleus, and the DNA floats free in the cytoplasm.

2. What is a prokaryotic cell?

   Answer: A cell without a defined nucleus (DNA floats free in the cytoplasm). No membrane-bound organelles. Simpler and more ancient. Examples: bacteria and archaea (primitive microorganisms). — Prokaryote comes from the Greek pro (before) + karyon (nucleus). Bacteria appeared 3.5 billion years ago according to evolutionists. The genetic material is in the form of a single circular chromosome. They have ribosomes and a cell wall (peptidoglycan in bacteria). Size 1-10 µm (10x smaller than eukaryotes). Reproduction by simple binary fission without mitosis.

3. Name 3 differences between an animal cell and a plant cell.

   Answer: The plant cell has: 1) a cell wall (cellulose); 2) chloroplasts (photosynthesis); 3) a large central vacuole. The animal cell does not have these 3 characteristic structures. — The cell wall gives the plant rigidity (wood, stem). Chloroplasts contain chlorophyll (green color) which carries out photosynthesis. The central vacuole stores water/nutrients - it can take up 80% of the cell. The animal cell has only a thin membrane, no chloroplast (it does not photosynthesize), and small vacuoles. The animal cell has centrioles, which the plant cell does not (related to division).

4. What are stem cells? What is their importance?

   Answer: Stem cells: undifferentiated cells that can become any type of cell (totipotent/pluripotent). Importance: they regenerate tissues and treat serious diseases. — Totipotent cells (zygote) become any cell, including the placenta. Pluripotent cells (embryonic) become any tissue, but not the placenta. Multipotent cells (adult bone marrow) become only a few lineages. Current treatments: leukemia, paralysis, severe burns. Research: Alzheimer's, Parkinson's, diabetes. There is ethical controversy over embryos in modern scientific research.

5. Name 3 functions of the plasma membrane.

   Answer: 1) Protection (it surrounds the cell); 2) Selective permeability (it controls entry/exit); 3) Recognition (receptors for hormones and external signals). — The membrane is a lipid bilayer with embedded proteins (the Fluid Mosaic Model, Singer-Nicolson 1972). Selective permeability allows water and gases through freely but controls glucose and ions. Membrane receptors capture signals such as insulin, neurotransmitters, and hormones. The glycocalyx on the surface identifies the cell as 'self' versus 'foreign' in the human immune system.

6. Explain the following forms of selective permeability: osmosis and diffusion.

   Answer: Diffusion: a solute moves from the more concentrated medium to the less concentrated one. Osmosis: water passes through a semipermeable membrane from the less concentrated medium to the more concentrated one. — Diffusion is the random movement of molecules following the concentration gradient - example: a gas spreading through the air. Osmosis involves only water - moving in the opposite direction to the solute, balancing the concentrations. An isotonic solution (equal) = no flow. Hypertonic (more solute outside) = the cell shrinks. Hypotonic (more solute inside) = the cell swells and can burst.

7. Explain the following forms of non-selective permeability: phagocytosis and pinocytosis.

   Answer: Phagocytosis: the cell 'eats' a solid particle (bacteria, debris) by engulfing it. Pinocytosis: the cell 'drinks' liquid, forming a vesicle. Both are forms of endocytosis. — Phagocytosis comes from the Greek phagein (to eat). Macrophages of the immune system phagocytize invading bacteria. Pinocytosis (pinein = to drink) takes in dissolved nutrients. The vesicle that forms goes to the lysosome, where enzymes digest its contents. The reverse is exocytosis (the cell releases substances). Both consume ATP; they are active processes because they use the cell's energy.

8. What is active transport and passive transport?

   Answer: Passive: along the gradient, without using ATP (osmosis, diffusion). Active: against the gradient, using ATP (sodium-potassium pump). — The sodium-potassium pump (Na+/K+ ATPase) is the main example of active transport — it spends 1 ATP for every 3 Na+ pumped out and 2 K+ pumped in. It maintains the membrane potential, essential for neurons. Passive transport is spontaneous, following entropy. Secondary active transport uses the gradient created by the pump as fuel to move other molecules.

9. What are the 4 parts of a cell nucleus? What is the importance of each one?

   Answer: Nuclear envelope (karyotheca), nucleoplasm (fluid), chromatin (DNA+proteins), and nucleolus (ribosomal RNA). They command everything in the cell. — The nuclear envelope is double, with pores for exchange with the cytoplasm. The nucleoplasm is a gel in which the chromatin floats. Chromatin condenses into chromosomes during cell division (mitosis). The nucleolus is a factory of ribosomes that will synthesize proteins. The nucleus is the 'brain' of the cell — all the genetic information that controls cellular functions is stored there centrally.

10. Name the functions of the following cytoplasmic organelles:
    • Mitochondrion
    • Centriole
    • Golgi complex
    • Rough Endoplasmic Reticulum
    • Smooth Endoplasmic Reticulum
    • Lysosome
    • Ribosome
    • Peroxisome

    Answer: 1) Mitochondrion: it is the cell's power plant; it carries out cellular respiration and produces ATP, the main source of energy. 2) Centriole: organizes the microtubules and takes part in cell division, guiding the separation of chromosomes; it also forms cilia and flagella. 3) Golgi complex: receives, modifies, packages, and distributes proteins and other substances produced by the cell, forming secretory vesicles. 4) Rough Endoplasmic Reticulum: has ribosomes attached to it and acts in protein synthesis. 5) Smooth Endoplasmic Reticulum: has no ribosomes; it synthesizes lipids, takes part in detoxifying substances, and in storing calcium. 6) Lysosome: contains digestive enzymes that perform intracellular digestion, breaking down particles and old organelles. 7) Ribosome: carries out protein synthesis from messenger RNA. 8) Peroxisome: detoxifies harmful substances and breaks down fatty acids, neutralizing hydrogen peroxide. — The mitochondrion is the 'power plant' (it has its own DNA, inherited maternally). Centrioles form the mitotic spindle. The Golgi modifies proteins for shipping. The Rough ER has ribosomes attached (protein synthesis). The Smooth ER synthesizes lipids and detoxifies drugs. Lysosomes have digestive enzymes. Peroxisomes break down fatty acids and neutralize toxic peroxide.

11. What is the importance of cilia and flagella?

    Answer: Cilia and flagella are structures for cellular movement. Cilia: small and numerous (they wave). Flagella: long and few (they whip). Locomotion and capture. — The human sperm cell uses a flagellum (90 µm) to swim to the egg at 0.1 mm/s. The cilia of the respiratory tract move mucus with dust particles outward. Paramecium (a protozoan) uses cilia to swim. Internal structure: 9+2 microtubules (axoneme). Movement consumes ATP. Without respiratory cilia, lung infections increase greatly.

12. Identify, by means of photos or drawings, 5 different types of cells (such as muscle, bone, cartilage, fat, leukocyte, red blood cell, neuron, etc.).

    Answer: Muscle cells have sarcomeres (contractile proteins). Bone cells (osteocytes) sit in lacunae within the bone. Cartilage cells (chondrocytes) produce an elastic matrix. Fat cells store fat. Red blood cells (without a nucleus in humans) carry oxygen. Neurons have a cell body + dendrites + axon. Leukocytes defend the body. Each one specializes in a specific function.