Assessment
1. What is the importance of the nucleus in a cell?
Answer: The nucleus is the control center of the cell and contains the cell’s DNA. DNA stores the instructions for making all of the proteins needed by the cell.
2. What is the function of ribosomes in the cytoplasm?
Answer: Ribosomes are small organelles in the cytoplasm that synthesize or assemble proteins using genetic information from mRNA (messenger ribonucleic acid).
3. Describe the process of active transport.
Answer: Active transport is an important mechanism that moves substances or ions across the cell membrane against the concentration gradient. It requires cellular energy in the form of ATP (adenosine triphosphate). Membrane proteins, such as “pumps” or “carriers,” bind with the substances to be transported and use the energy from ATP to transport the substances across the membrane.
4. What is the purpose of cell signaling in the body?
Answer: Cell signaling is the process by which cells communicate with each other to coordinate activities and respond to changes in the environment. It ensures that individual cells or groups of cells can send and receive chemical signals or messages to alter their behavior or function in a controlled manner.
5. Provide examples of positive feedback mechanisms in the human body.
Answer:
- Childbirth: The hormones oxytocin and prostaglandin cause increased uterine contractions during labor, leading to the birth of the baby. Once birth begins, it continues until the baby is delivered.
- Blood clotting: When blood is exposed to air or an injured site, platelets aggregate and release clotting factors, ultimately forming a clot that prevents bleeding. The clotting continues until the blood vessel is sealed and the bleeding stops.
- Lactation: Suckling by the infant stimulates the production of the hormone prolactin, which promotes milk production in the mammary glands of the mother. The more the infant suckles, the more prolactin is produced, increasing milk production.
6. Explain the concept of apoptosis, and provide an example of its role in the body.
Answer: Apoptosis, also known as programmed cell death, is a process by which the body’s cells die in a controlled manner. It is essential for maintaining tissue homeostasis, eliminating damaged or dysfunctional cells, and ensuring proper development and functioning of organisms.
Example: During embryonic development, the cells that will form fingers and toes undergo apoptosis, leading to the separation and distinct formation of each digit. This process ensures the proper development of body structures.
7. Describe the key components of the plasma membrane and their functions.
Answer: The plasma membrane, also known as the cell membrane, is a thin phospholipid bilayer that encloses the cell and regulates what enters and exits the cell.
- Phospholipids: They form the basic structure of the membrane and create a semi-permeable barrier.
- Proteins: They are embedded in the phospholipid bilayer and perform various functions such as cell signaling, transport of molecules, and adhesion.
- Carbohydrates: They are attached to the proteins and lipids on the outer surface of the membrane and play roles in cell recognition and cell-cell communication.
- Cholesterol: It is found within the membrane and helps in maintaining the membrane’s fluidity and stability.
8. State the principle of diffusion and explain how it is important for cells.
Answer: Diffusion is the passive movement of particles from an area of higher concentration to an area of lower concentration without the use of energy. It occurs due to the random motion of particles, and its rate depends on temperature, concentration gradient, and surface area.
Diffusion is crucial for cells as it allows important molecules and substances to move in and out of cells. It facilitates the exchange of nutrients, waste products, gases, and other molecules necessary for cell function and survival.
9. How do lysosomes function in the cell?
Answer: Lysosomes are small membrane-bound organelles that contain various hydrolytic or digestive enzymes. They are involved in:
- Intracellular digestion: Lysosomes fuse with endocytic vesicles and food vacuoles to digest ingested material and worn-out or damaged cell components.
- Recycling: They break down and recycle the cellular components, reusing the obtained molecules within the cell.
- Defense against pathogens: They can fuse with pathogens or foreign particles that have entered the cell and degrade them, preventing infection and protecting the cell.
10. Define endocytosis and explain its different types.
Answer: Endocytosis is the process by which cells take in materials from the external environment by engulfing them with the cell membrane. There are three main types of endocytosis:
- Phagocytosis: Cell extensions called pseudopodia engulf solid particles, microorganisms, or debris, forming a vacuole called a phagosome.
- Pinocytosis (Cell drinking): The cell membrane invaginates and forms small vesicles called pinosomes, leading to the uptake of fluids and dissolved materials.
- Receptor-mediated endocytosis: Specific molecules bind to receptors on the cell membrane and trigger the formation of clathrin-coated pits, which then invaginate and form vesicles containing the bound molecules.