Membrane moves
Vesicle delivery
Energy and enzymes
Cell life and division
Chromosome shuffle
100
Sketch a phospholipid bilayer. Label the parts that interact with water and the parts that avoid water.
Hydrophilic heads face the watery fluid on both sides. Hydrophobic tails point inward, away from water. A bilayer has two layers of phospholipids.
100
A cell folds its membrane inward and encloses material in a small sac. Is this endocytosis or exocytosis? What is the sac called?
Endocytosis brings material into the cell. The membrane-bound sac is a vesicle.
100
Compare a rolling ball with a stretched rubber band. Which shows kinetic energy and which stores potential energy?
Rolling ball: kinetic energy, the energy of motion. Stretched rubber band: stored potential energy. Chemical bonds also store potential energy.
100
Draw chromosomes lined up individually across the middle of a mitotic cell. Name the phase and explain what happens next.
Metaphase. Next, in anaphase, sister chromatids separate and move toward opposite poles. Homologous pairs do not line up together in mitosis.
100
A diploid animal has 14 chromosomes in its body cells. How many should a normal gamete have? Name the cell formed when two gametes fuse.
Each gamete has 7 chromosomes and is haploid. Fertilization joins two gametes to form a diploid zygote with 14 chromosomes.
200
Oxygen crosses directly through a membrane. A sugar moves through a carrier protein. Both move from higher to lower concentration. Name each process.
Oxygen: simple diffusion. Sugar: facilitated diffusion. Both are passive and move down a concentration gradient without direct ATP use. A carrier alone does not make transport active.
200
An amoeba takes in a large food particle. Another cell takes in tiny droplets of surrounding fluid. Name both types of uptake.
Large particle: phagocytosis, or cell eating. Fluid droplets: pinocytosis, or cell drinking. Both are forms of endocytosis.
200
During exercise, chemical energy becomes movement and heat. Does this violate the first law of thermodynamics? Explain.
No. Energy changes form while total energy is conserved. The cell does not create or destroy energy.
200
One cell leaves the division cycle but remains alive and carries out its job. Another cell activates an orderly self-destruction program. Name both states or processes.
The nondividing cell is in G0. The orderly cell-death process is apoptosis, which supports development and tissue maintenance. G0 is not cell death.
200
Compare mitosis and meiosis starting with a diploid cell: how many nuclear divisions occur, and are the final nuclei haploid or diploid?
Mitosis: one nuclear division, diploid daughter nuclei. Meiosis: two nuclear divisions, haploid final nuclei. Typical mitosis yields two cells. Typical meiosis produces four haploid nuclei with genetic differences.
300
A membrane lets water cross but blocks a dissolved sugar. One side contains more sugar. Which way will water move overall, and what membrane channels can help it cross?
What is osmosis? Water moves overall toward the side with more dissolved sugar, assuming equal pressure. Aquaporins are channels that allow water to cross more easily.
300
A gland cell packages a hormone into a vesicle. Describe how the hormone can leave the cell.
The vesicle moves to and fuses with the plasma membrane, releasing its contents outside by exocytosis.
300
A cell builds ATP from smaller components. Name those components and explain whether this step requires or releases energy.
ADP and inorganic phosphate combine to form ATP with an energy input. ATP hydrolysis back to ADP and phosphate releases usable free energy overall and can couple to cellular work.
300
A skin cell has 18 chromosomes before DNA replication. After normal mitosis and division of the cytoplasm, how many cells form and how many chromosomes does each have?
Two daughter cells, each with 18 chromosomes. Mitosis preserves chromosome number. DNA replication creates sister chromatids but does not double chromosome number when counted by centromeres before separation.
300
Two chromosomes carry the same kinds of genes in the same locations, but may carry different versions. What are they? What do we call the paired unit when each has been duplicated?
They are homologous chromosomes. When duplicated homologs pair in meiosis I, they form a bivalent or tetrad with four chromatids. Sister chromatids are the two copies of one duplicated chromosome.
400
A cell already has more of an ion inside than outside, yet it continues bringing that ion in. Explain what makes this different from diffusion.
It moves the ion against its concentration gradient, so it requires an energy source. This is active transport. Diffusion moves substances down their gradient.
400
Draw a vesicle entering a cell, then show a vesicle releasing material. Label the two processes as you illustrate them.
Entering: endocytosis, with membrane folding inward. Releasing: exocytosis, with a vesicle fusing with the membrane.
400
Sketch an enzyme, a fitting substrate, and a competing molecule that blocks the same location. Label the binding location and explain why less product forms.
The substrate binds the active site. A competitive inhibitor can occupy that site, reducing substrate binding and product formation. The enzyme is not necessarily destroyed. Products are the molecules released after the reaction.
400
A cell separates its nuclear material into two nuclei but never splits its cytoplasm. Name the completed process, name the missing process, and describe the result.
Mitosis is complete, but cytokinesis is missing. The result is one cell with two nuclei. Mitosis divides nuclear material. Cytokinesis divides the cytoplasm.
400
Draw one duplicated chromosome and label its sister chromatids. Then draw its homolog beside it. Are the two homologs guaranteed to carry identical gene versions?
Each duplicated chromosome has two sister chromatids joined at a centromere. Homologs carry the same genes at corresponding locations but can carry different alleles.
500
A plant cell passes materials directly to its neighbor through a tiny passage across their cell walls. Name the passage and explain why an animal cell would not have it.
Plasmodesmata are channels connecting neighboring plant cells through their walls. Animal cells lack cell walls and plasmodesmata. Animal cells can communicate through gap junctions.
500
A student says, “If something crosses a membrane without going directly through the phospholipids, it must use a vesicle.” Correct the claim with an example.
Facilitated diffusion uses a channel or carrier protein without a vesicle. Vesicle transport instead encloses material in a membrane-bound sac. Example: water through an aquaporin or a sugar through a carrier.
500
Use the energy diagram: identify the pathway with an enzyme. Does the overall reaction release energy or need a net input? Would an enzyme change that overall energy difference?
The lower peak represents the enzyme-catalyzed pathway because it has lower activation energy. Products lie below reactants, so the reaction releases free energy overall: exergonic. An enzyme changes the barrier, not the overall free-energy difference. Endergonic reactions require a net energy input.
500
A bacterium copies its DNA and divides into two cells. Name this process and explain why the cell does not need mitosis.
Binary fission. Bacteria have no membrane-bound nucleus and do not use the eukaryotic mitotic spindle. They still copy and separate their DNA before dividing.
500
Why can one primary sperm-producing cell yield four functional sperm, while one primary egg-producing cell generally yields one functional egg?
Sperm production divides the cytoplasm more evenly among four haploid products. Egg production divides it unequally, concentrating cytoplasm in one functional egg and forming small polar bodies. Both produce haploid gametes.