cells as the basis of life

Cell theory

Cell theory

idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells

Cell membrane

the semipermeable membrane surrounding the cytoplasm of a cell.

Cytoplasm

A jellylike fluid inside the cell in which the organelles are suspended

Organelle

specialized structure that performs important cellular functions within a eukaryotic cell

Phospholipid

A molecule that is a constituent of the bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.

Fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

Glycoproteins

proteins that have carbohydrates covalently bonded to them

Glycolipids

a lipid with one or more covalently attached carbohydrates

Channel proteins

provide corridors that allow a specific molecule or ion to cross the membrane

Globular proteins

these are compact, generally rounded, and soluble in water.

Hydrophobic

Having an aversion to water; tending to coalesce and form droplets in water.

Hydrophyllic

water loving (dissolvable) area of plasma membrane where polar heads point out.

Cholesterol

A lipid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.

Prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.

Eukaryotic cell

A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Examples of organisms with these cells are protists, plants, fungi, and animals.

Nucleus

A part of the cell containing DNA and RNA and responsible for controlling growth and reproduction of the cell

Nucleolus

A dense region found inside the nucleus that produces ribosomes

Mitochondrion

Cell organelle that converts the chemical energy stored in food into compounds that are more convenient for the cell to use

Chloroplast

Organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy

Endoplasmic Reticulum

A system of membranes that is found in a cell's cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids.

Golgi apparatus

A system of membranes that modifies and packages proteins for export by the cell

Lysosome

A small, round cell structure containing chemicals that break down large food particles into smaller ones.

Peroxisome

Contains oxidase enzymes that detoxify alcohol, hydrogen peroxide, and other harmful chemicals

Cytoskeleton

A network of long protein strands in the cytosol that helps support the cell

Vacuole

Cell organelle that stores materials such as water, salts, proteins, and carbohydrates

Vesicle

Small membrane-bound sac that functions in moving products into, out of, and within a cell.

Ribosome

Cytoplasmic organelles at which proteins are synthesized.

Nuclear envelope

A double membrane that surrounds the nucleus in the cell

Nuclear pores

structures in the nuclear envelope that allow passage of certain materials between the cell nucleus and the cytoplasm

Chromatin

Substance found in eukaryotic chromosomes that consists of DNA tightly coiled around histone proteins

Chromosomes

Threadlike structures made of DNA molecules that contain the genes

Cristae

Infoldings of the inner membrane of a mitochondrion that houses the electon transport chain and the enzyme catalyzing the synthesis of ATP.

Plastid

A group of membrane‐bound organelles commonly found in photosynthetic organisms and mainly responsible for the synthesis and storage of food.

Thylakoid

A flattened membrane sac inside the chloroplast, used to convert light energy into chemical energy.

Grana

A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis

Stroma

The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

Chlorophyll

A green pigment found in the chloroplasts of plants, algae, and some bacteria

Pigments

Molecules that absorb, reflect, or transmit light.

Secretion

A process by which substances are produced and discharged from a cell, gland, or organ for a particular function in the organism or for excretion.

Exocytosis

Release of substances out a cell by the fusion of a vesicle with the membrane.

Endocytosis

A process in which a cell engulfs extracellular material through an inward folding of its plasma membrane.

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Phagocytosis

A type of endocytosis in which a cell engulfs large particles or whole cells

Rough Endoplasmic Reticulum

An endomembrane system covered with ribosomes where many proteins are assembled for transport.

Smooth Endoplasmic Reticulum

An endomembrane system where lipids are synthesized, calcium levels are regulated, and toxic substances are broken down.

Microfilaments

Long, thin fibers that function in the movement and support of the cell

Microtubules

Spiral strands of protein molecules that form a tubelike structure

Intermediate filaments

Threadlike proteins in the cell's cytoskeleton that are roughly twice as thick as microfilaments

Spindle apparatus

structure made of spindle fibers, centrioles, and aster fibers that is involved in moving and organizing chromosomes before the cell divides

Cell wall

A rigid structure that surrounds the cell membrane and provides support to the cell

Autotroph

An organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide.

Heterotroph

An organism deriving its nutritional requirements from existing complex organic substances.

Photosynthesis

Process by which plants and some other organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches

Cellular respiration

Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

Glycolysis

A metabolic process that breaks down carbohydrates and sugars through a series of reactions to either pyruvic acid or lactic acid and release energy for the body in the form of ATP

Krebs cycle

Second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions

Citric acid cycle

Also known as the Krebs cycle. Completes the breakdown of glucose by oxidizing a derivative of pyruvate to carbon dioxide.

Aerobic respiration

Respiration that requires oxygen

Anaerobic respiration

Respiration that does not require oxygen

Facultative anaerobes

can survive with or without oxygen

ATP (adenosine triphosphate)

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

ADP (adenosine diphosphate)

Nucleotide with two phosphate groups that can accept another phosphate group and become ATP.

Phosphate group

A chemical group consisting of a phosphorus atom bonded to four oxygen atoms; important in energy transfer.

Pyruvate

Organic compound with a backbone of three carbon atoms. Two molecules form as the end products of glycolysis

Carbon dioxide and water

Products of cellular respiration

Glucose and oxygen gas

Products of photosynthesis

Fermentation

A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such as ethyl alcohol or lactic acid.

Ethyl alcohol (ethanol)

Ethyl alcohol is a by-product of fermentation. Two ethyl alcohol molecules are produced for every one glucose that is broken down. Yeast cells and some bacteria make ethanol and carbon dioxide during anaerobic respiration.

Lactic acid

Product of fermentation in many types of cells, including human muscle cells

Diffusion

Movement of solute molecules from an area of higher concentration to an area of lower concentration.

Osmosis

Diffusion of water through a selectively permeable membrane

Concentration gradient

Difference in the concentration of a substance from one location to another

Facilitated diffusion

Movement of specific molecules across cell membranes through protein channels with the concentration gradient

Active transport

Energy-requiring process that moves material across a cell membrane against a concentration gradient

Aquaporin

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane

Water potential

The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure.

Passive transport

The movement of substances across a cell membrane without the use of energy by the cell

Turgidity

The state of being turgid or swollen, especially due to high fluid content.

Flaccid

Limp, not firm or strong (If a plant is not watered enough, its leaves become droopy)

Solute

A substance that is dissolved in a solution.

Solvent

A liquid substance capable of dissolving other substances

Surface area to volume ratio

A variable that decreases as cells grow, so that it sets a limit to the size of cells.

Metabolic pathway

A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.

Exergonic

Chemical reactions that release energy

Endergonic

A chemical reaction that requires the input of energy in order to proceed.

Active site

The part of an enzyme or antibody where the chemical reaction occurs.

Antibiotic

A chemical that kills bacteria or slows their growth without harming body cells.

Poison

A substance that causes illness, injury or death if taken into the body or produced within the body.

Enzyme

A type of protein that speeds up a chemical reaction in a living thing

Enzyme inhibition

Process in which a molecule binds to enzymes and inhibits their activity

Proton pump

An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.

Zygote

A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

Somatic cells

Any cells in the body other than reproductive cells

Gamete

Specialized cell involved in sexual reproduction

Homologous

Term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent

Germ cells

Reproductive cells that give rise to sperm and ovum

Haploid

An organism or cell having only one complete set of chromosomes

Diploid

Containing two complete sets of chromosomes, one from each parent.

Binary fission

A form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size

Mitosis

Cell division in which the nucleus divides into nuclei containing the same number of chromosomes