Bio: Cell Biology DEFINITIONS

What is a eukaryote?

An organism made up of eukaryotic cells, which are complex and contain a nucleus along with membrane-bound organelles (e.g. animal and plant cells).

What is a prokaryote?

A single-celled organism made up of a prokaryotic cell, which is smaller, simpler, and lacks a nucleus and membrane-bound organelles (e.g. bacteria).

What is the function of the nucleus?

Contains genetic material (DNA) that controls the activities of the cell.

What is the function of cytoplasm?

A gel-like substance where most of the chemical reactions happen; contains enzymes that control these reactions.

What is the function of the cell membrane?

Holds the cell together and controls the movement of substances in and out of the cell.

What is the function of mitochondria?

Structures where most of the reactions for aerobic respiration take place, transferring energy that the cell needs to work.

What is the function of ribosomes?

Site where proteins are synthesized (protein synthesis).

What is the function of the cell wall?

A rigid structure made of cellulose that supports and strengthens plant and algal cells.

What is the function of the permanent vacuole?

Contains cell sap (a weak solution of sugar and salts) to maintain cell turgidity and support.

What is the function of chloroplasts?

Structures where photosynthesis occurs to produce food for the plant; contain chlorophyll which absorbs light.

What is a plasmid?

A small, circular ring of DNA found floating freely in the cytoplasm of bacterial cells.

What is magnification?

How many times larger an image appears compared to the real size of the object.

What is resolution?

The ability to distinguish between two separate points that are close together, determining the clarity of an image.

What is the formula for magnification?

$\text{Magnification} = \frac{\text{Image size}}{\text{Real size}}$

What is cell differentiation?

The process by which a cell changes to become specialized for a specific function by developing different subcellular structures.

What is a stem cell?

An undifferentiated cell that is capable of dividing to produce more undifferentiated cells and differentiating into various specialized cell types.

What is the function of a sperm cell and how is it specialized?

Specialized for reproduction to deliver male DNA to female DNA; features a long tail and streamlined head for swimming, many mitochondria for energy, and enzymes in its head to digest through the egg cell membrane.

What is the function of a nerve cell and how is it specialized?

Specialized for rapid electrical signaling; features long axons to cover distance and branched connections (dendrites) to form a network with other nerve cells.

What is the function of a muscle cell and how is it specialized?

Specialized for rapid contraction; features long fibers so they have space to contract and abundant mitochondria to generate energy.

What is the function of a root hair cell and how is it specialized?

Specialized for absorbing water and mineral ions from soil; features long hair-like projections that give a large surface area for absorption.

What is the function of phloem cells and how are they specialized?

Specialized for transporting food substances (sucrose) around plants; formed of long cells joined end-to-end with pores/sieve plates and few subcellular structures so stuff can flow through.

What is the function of xylem cells and how are they specialized?

Specialized for transporting water and mineral ions up plants; formed of dead cells joined end-to-end, hollow in the center, and strengthened by lignin.

What is a chromosome?

Coiled-up length of DNA found in the nucleus that carries a large number of genes controlling characteristics.

What is the cell cycle?

A series of stages that body cells go through as they divide to produce new cells for growth, development, and repair.

What is mitosis?

The stage of the cell cycle where the cell's nucleus and duplicated chromosomes divide to produce two genetically identical daughter cells with the same number of chromosomes as the parent cell.

What is binary fission?

A simple cell division process in prokaryotic cells (bacteria) where circular DNA and plasmids replicate, the cell enlarges while DNA strands move to opposite poles, and the cytoplasm divides to form two genetically identical daughter cells.

What is mean division time?

The average amount of time it takes for one bacterial cell to divide into two.

What is a culture medium?

A liquid (nutrient broth) or solid gel (agar jelly) containing carbohydrates, minerals, proteins, and vitamins used to grow microorganisms in a lab.

What is an inhibition zone?

The clear region around an antibiotic or antiseptic disc on an agar plate where bacteria have died or failed to grow.

What is the function of a control disc in antibiotic testing?

A paper disc soaked in sterile water used to confirm that any difference in bacterial growth inhibition is due to the chemical alone rather than the paper disc.

What are aseptic techniques?

Sterilization procedures (such as flaming inoculating loops, sterilizing Petri dishes, and lightly taping lids) used to prevent contamination by unwanted pathogens.

What is an embryonic stem cell?

An undifferentiated cell from an early human embryo that has the potential to divide and differentiate into any specialized cell type in the human body.

What is an adult stem cell?

An undifferentiated cell found in specific places like bone marrow that can only differentiate into certain cell types (e.g. blood cells).

What is therapeutic cloning?

A process where an embryo is produced with the exact same genetic information as a patient, allowing its stem cells to be used for medical treatments without risk of immune rejection.

What is a meristem?

Tissue in the growing regions of plants (roots and shoots) that contains stem cells capable of differentiating into any type of plant cell throughout the plant's life.

What is diffusion?

The net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient.

What is a concentration gradient?

The difference in concentration of a substance between two regions.

What is osmosis?

The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.

What is a partially permeable membrane?

A membrane with microscopic pores that allows tiny molecules (like water) to pass through while blocking larger solute molecules (like sucrose or starch).

What is the formula for percentage change in mass in osmosis experiments?

$\text{Percentage Change} = \frac{\text{Final mass} - \text{Initial mass}}{\text{Initial mass}} \times 100$

What is active transport?

The movement of substances from a lower concentration to a higher concentration against a concentration gradient, requiring energy from respiration[cite: 16].

How do root hair cells use active transport?

They absorb mineral ions from a very dilute solution in the soil against a concentration gradient into the plant for healthy growth[cite: 16].

How is active transport used in the human gut?

It allows nutrients like glucose to be absorbed into the bloodstream from the gut, even when the concentration of nutrients in the blood is higher than in the gut[cite: 16].

What is surface area to volume ratio (SA:V)?

A ratio comparing the total outer surface area of an organism to its internal volume, which determines how efficiently substances can be exchanged with its environment[cite: 16].

Why do single-celled organisms not need specialized exchange surfaces?

They have a large surface area to volume ratio, allowing gases and dissolved substances to diffuse directly into and out of the cell across the membrane quickly enough to meet their needs[cite: 16].

Why do multicellular organisms require specialized exchange surfaces?

They have a small surface area to volume ratio, so diffusion across their outer surface alone is too slow to supply their entire volume[cite: 16].

What general features adapt exchange surfaces for maximum efficiency?

A thin membrane for a short diffusion distance, a large surface area so lots of substance diffuses at once, and in animals, an efficient blood supply and ventilation[cite: 16].

What are alveoli and how are they adapted for gas exchange?

Tiny air sacs in the lungs where oxygen and carbon dioxide are exchanged; adapted by having an enormous surface area, a moist lining, very thin walls, and a rich capillary network[cite: 17].

What are villi and how are they adapted for absorption in the small intestine?

Microscopic finger-like projections that increase the surface area for absorbing digested food; adapted by having a single layer of surface cells and a very good blood supply[cite: 17].

What are stomata and how do they function in leaf gas exchange?

Little holes on the underside of leaves controlled by guard cells that allow carbon dioxide to diffuse into the leaf and oxygen and water vapour to diffuse out[cite: 17].

How is the internal structure of a leaf adapted for diffusion?

The leaf has a flattened shape to increase surface area and air spaces inside to maximize the chance of carbon dioxide diffusing into photosynthetic cells[cite: 17].

What are gill filaments and lamellae?

Structures in fish gills that provide a large surface area for gas exchange; lamellae cover the filaments, contain lots of capillaries, and feature a thin surface layer of cells[cite: 17].

How does the countercurrent mechanism in fish gills maximize gas exchange?

Blood flows through the lamellae in one direction while water flows over them in the opposite direction, maintaining a steep concentration gradient along the full length of the capillary[cite: 17].