Cell theory & MAgnification
If a scientist discovered a new living organism that does not consist of cells, would this disprove the cell theory?
Yes. One of the three main principles of cell theory states that all living organisms are composed of one or more cells. If a truly living organism lacked cells, the theory would need to be revised.
A cell is placed in a solution and shrinks. What can you logically conclude about the solution?
It is hypertonic. Water moves out by osmosis, indicating the external solution has a higher solute concentration.
A network of flattened membrane sacs covered with ribosomes on its cytoplasmic surface.
Rough Endoplasmatic retticulum
Why is mitosis necessary for multicellular organisms beyond growth?
It is essential for tissue repair and maintaining genetic stability. Damaged cells are replaced, and identical DNA is ensured.
Two patients need cell replacement: one for skin, one for spinal cord. Why are embryonic stem cells more useful than adult stem cells?
They are pluripotent and can differentiate into any cell type. Adult stem cells are multipotent with limited potential.
A scientist observes a structure capable of metabolism and homeostasis but unable to reproduce. Should it be classified as a cell?
No. Cells must show all characteristics of life, including reproduction. This might be an organelle or a non-living system.
Sodium ions cannot cross a membrane despite a steep concentration gradient. What does this suggest about the membrane transport mechanism?
It likely requires active transport. The inability to diffuse despite a gradient implies a need for ATP and carrier proteins.
A dense, spherical structure found inside the nucleus of eukaryotic cells. Its main function is to produce ribosomal RNA.
Nucleolus
During which phase of mitosis do sister chromatids separate and move to opposite poles of the cell, and why is this step essential for cell division?
This occurs during anaphase. The centromeres split, and sister chromatids are pulled apart by spindle fibers to opposite poles. This separation is essential to ensure that each daughter cell receives an identical set of chromosomes, maintaining genetic consistency.
Why are embryonic stem cells considered more versatile than adult stem cells?
Embryonic stem cells are pluripotent, meaning they can differentiate into almost any cell type in the body. In contrast, adult stem cells are usually multipotent, so they can produce only a limited range of cell types related to their tissue of origin.
A cell image in a textbook measures 5 cm in diameter. The actual diameter of the cell is 50 µm. What is the magnification of the image?
5 cm = 50 mm = 50 000 µm
Magnification = Image size ÷ Actual size
50 000 µm ÷ 50 µm= 1000×
The image is magnified 1000 times.
Explain how facilitated diffusion differs from simple diffusion across a cell membrane.
Facilitated diffusion requires specific membrane proteins (channel or carrier proteins) to help polar or large molecules cross the membrane, while simple diffusion occurs directly through the phospholipid bilayer without assistance. Both are passive processes that do not require energy and move substances down their concentration gradient.
Why do cells tend to be small in size?
Cells are small because a higher surface area to volume ratio allows for more efficient exchange of materials (like nutrients and waste) with the environment. As a cell grows, its volume increases faster than its surface area, reducing this ratio and making transport less efficient. Therefore, smaller cells maintain a favorable ratio for effective diffusion and cellular function.
A tissue sample shows 60% of cells in interphase and 40% in mitosis. What can be inferred about the cell cycle length?
Interphase is longer than mitosis. Most of the cell’s life is spent in growth and DNA replication.
A patient with damaged heart muscle is treated with stem cells that regenerate functional tissue. What property of stem cells makes this possible?
Their capacity for self-renewal and differentiation. They can replace lost cells and restore function.
Two cells are observed under a microscope: Cell A has a large central vacuole, a cell wall, and chloroplasts. Cell B has many small vacuoles, centrioles, and no cell wall. What can you conclude about the type of each cell, and how do these structural differences relate to their functions?
Cell A is a plant cell — the large vacuole helps maintain turgor pressure, the cell wall provides structural support, and chloroplasts allow photosynthesis.
Cell B is an animal cell — the presence of centrioles indicates a role in cell division, and the absence of a cell wall allows more flexible cell shapes and movement.
The fluid mosaic model describes the structure of the plasma membrane. Explain why the membrane is described as both "fluid" and "mosaic."
It is called "fluid" because the phospholipids and proteins can move laterally within the layer, giving the membrane flexibility. It is "mosaic" because it consists of different components — phospholipids, proteins, cholesterol, and carbohydrates — arranged in a varied pattern within the bilayer.
Which organelle is present in plant cells but not in animal cells, and how does its structure relate to its function?
The chloroplast is present only in plant cells. It contains thylakoid membranes with chlorophyll arranged in stacks (grana), which increase the surface area for light-dependent reactions of photosynthesis.
If the spindle fibers failed to attach to centromeres during metaphase, what would happen?
Chromosomes would not separate correctly, leading to aneuploidy. Proper attachment ensures equal distribution
Why are stem cells from umbilical cord blood less controversial than embryonic stem cells?
They do not involve embryo destruction. They are collected post-birth without ethical concerns.
Mitochondria and chloroplasts contain their own DNA and divide independently. What logical conclusion can be drawn about their evolutionary origin?
They likely originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells — evidence supporting the endosymbiotic theory.
If phospholipids in a membrane had only saturated fatty acids, how would the membrane’s properties change?
It would become less fluid and more rigid. Saturated tails pack tightly, reducing membrane flexibility and permeability.
Why do pancreatic cells have more rough ER than red blood cells?
They secrete large amounts of protein (enzymes, hormones). Rough ER is needed for protein synthesis; RBCs lack organelles entirely.
A cell with 20 chromosomes undergoes mitosis. How many chromosomes will each daughter cell have?
Mitosis produces genetically identical daughter cells.
If stem cells divide indefinitely but stop differentiating, what problem could arise?
Tumor formation (cancer). Uncontrolled division without specialization can lead to malignancies.