AHSGE Review

J. Pollock

Spring 2007

Cell Structure and Function

What is homeostasis?

Homeostasis is the maintenance of the internal stability of a cell, organism, or population in its environment.

It is a characteristic of all living things. It allows organisms to survive in

extreme conditions.

How do cells maintain homeostasis?

The plasma membrane determines what will get in or stay out.

It is made of a combination of phospholipids and proteins.

Materials can enter and leave the cell through active or passive transport.

Compare active and passive transport. Active Transport

proton pumps, sodium-potassium pumps, coupled channels, endocytosis, and exocytosis

uses energy

Passive Transport does not use energy diffusion, osmosis, or

facilitated diffusion

Passive Processes

Diffusion is movement from high concentration to low concentration areas.

Osmosis a form of diffusion that involves polarity of molecules.

Facilitated diffusion involves transfer of specific particles through the cell membrane using channel proteins.

Passive Processes

Active Processes

Proton pumps move protons through internal plasma membranes of mitochondria and chloroplasts.

Sodium-potassium pumps move potassium into the cell and sodium out using ATP. It is the most important energy-using process in the human body.

Coupled channels use a sodium-potassium pump and a second channel to move sugar molecules.

Active Processes

Compare exocytosis and endocytosis. Exocytosis

dumping of excretions or waste

uses waste vaculoes to push matter outside cell

also involved in secretion of hormones

Endocytosis particle engulfed by

cell membrane requires energy pinocytosis

liquid with dissolved molecules

phagocytosis another cell or

fragment of organic matter

Endocytosis and Exocytosis

What are the functions of carbohydrates in cellular activities?

Carbohydrates are composed of hydrogen, carbon, and oxygen.

They store and transport energy for cellular activities.

Polysaccharides are linked carbohydrates that store and convert sugars. Starch is an example.

Carbohydrates

What are the functions of lipids in cellular activities?

Lipids do not dissolve in water. They are fats, oils, and waxes. They are components of the cell membrane and

store energy. Saturated fats contain the maximum number of

carbon and hydrogen molecules. Unsaturated fats have carbon-carbon double bonds

and contain fewer hydrogen atoms. Steroids are the hormones that control body

activities.

Lipids

What are the functions of proteins in cellular activities? Proteins have important structural functions. Collagen makes up skin, ligaments, tendons, and

bones. Enzymes assist in the chemical reactions of

metabolism. They speed up and slow down reactions without being used up themselves.

Amino acids are the building blocks of proteins. They make long chains called polypeptides.

Proteins also function as hormones and neurotransmitters to signal cells and regulate activity.

Proteins

What are the functions of nucleic acids in cellular activities?

Nucleic acids are long chains of nucleotides (5-carbon sugar with phosphate group and organic base).

They serve to store hereditary information that will later form new proteins.

Deoxyribonucleic acid (DNA) stores information in cells.

Ribonucleic acid (RNA) helps in the making of proteins.

DNA and RNA

Compare the reactions of plant and animal cells in various types of solutions.

Hypotonic Isotonic Hypertonic

Soluteconcentration in

environment lowerthan in cell

Soluteconcentration in

environment equalto that in cell

Soluteconcentration in

environmentgreater than in cell

Water moves intocell

Equal movement ofwater into and out

of cell

Water moves out ofcell

Cell bursts Volume maintained Cell shrivels

Explain how environment affects cellular activity. Protein receptors on the cell surface

signal the cytoplasm about the conditions of the cell’s environment.

The cytoplasm responds to the surface whether or not particles should be allowed into the cell.

The cell attempts to maintain homeostasis at all times.

How does fluid pressure affect biological systems?

Hypotonic Isotonic Hypertonic

Soluteconcentration in

environment lowerthan in cell

Soluteconcentration in

environment equalto that in cell

Soluteconcentration in

environmentgreater than in cell

Water moves intocell

Equal movement ofwater into and out

of cell

Water moves out ofcell

Cell bursts Volume maintained Cell shrivels

Describe the process of photosynthesis. Photosynthesis forms a continuous cycle

with cellular respiration. Carbon atoms are pulled from carbon

dioxide in the air and used to form carbohydrates and other organic compounds.

Hydrogen is extracted from water molecules, and oxygen is released as a by-product.

Describe the process of cellular respiration. Cellular respiration is the reverse of

photosynthesis. Hydrogen molecules from carbohydrates

are joined with oxygen to form water. Carbohydrates and organic molecules are

chemically broken down and used as energy sources.

Carbon dioxide is released as a by-product.

Photosynthesis and Cellular Respiration

What are the parts of the cell?

Who contributed to the cell theory? Robert Hooke discovered cells in 1665 while looking

at cork through a microscope. Anton van Leeuwenhoek discovered single-celled

protists in 1675 looking at pond water. In 1838 Matthias Schleiden determined that cells

compose all parts of a plant. Theodor Schwann applied this discover to animals one year later.

Rudolph Virchow determined that cells come only from other cells in 1858.

All of these individuals contributed to the cell theory.

Cell Theory

All living things are composed of one or more cells.

In organisms, cells are the basic units of structure and function.

Cells are produced only from existing cells.

Characteristics of Cells

Cell membrane or plasma membrane to separate contents from environment

cytoplasm (everything except genetic material)

ability to reproduce possession of genetic material

Compare prokaryotic and eukaryotic cells. Prokaryotes

single cell organisms no nucleus no internal membrane-

bound compartments very small few specialized

functions genetic material single,

circular molecule

Eukaryotes contain nucleus specific membrane-

bound organelles more complex function most multicellular contain highly

specialized cells

How are cells observed?

Cells are too small to be observed with the naked eye.

Cells must be small to accommodate the exchange of materials with the environment and the distribution of materials.

They are viewed using microscopes.

How do cells become more advanced structures? Single cells cluster into multicellular

organisms. Cells become more specialized, and a few

cells take over activities once performed by all cells.

Scientists believe eukaryotes developed from prokaryotes (bacteria) that were enveloped by larger cells. They eventually lost their ability to function separately.