How Cells

Function

Chapter 2 Review

All cells are made of the same elements.

◦ There are about 100 elements; 25 of them are necessary for life.

◦ The smallest unit of an element is the atom.

◦ Atoms bond together in chemical reactions to form molecules.

Chemical reactions take place inside cells.

All large molecules in living things contain carbon. Carbon atoms can form long chains, leading to a huge number of possible compounds. There are four types of large molecules.

◦ Carbohydrates- are sugar starch, and cellulose. They provide the cell with energy.

◦ Lipids- are fats, oils, and waxes that cannot mix with water. Lipids often provide cells with energy.

◦ Proteins- are made of smaller molecules- amino acids. Proteins control chemical reactions, support growth and repair of tissue, allow movement, fight infections, and deliver oxygen.

◦ Nucleic acids- hold the instructions for maintenance, growth, and reproduction of the cell. The two types are DNA and RNA.

Large molecules support cell functions.

A water molecule, which consists of two hydrogen atoms and one oxygen atom, is a polar molecule. Because its two sides have slightly different charges, water is an excellent solvent.

Cell membranes are composed of special lipids that have one end that repels water. Cell membranes have double layers of lipids. Both sides of a membrane have water-repellent ends facing out.

About two thirds of every cell is water.

All cells need energy!◦ Molecules store chemical energy in the bonds between their atoms.

Glucose is the energy source for most cells.

Some cells capture light energy. ◦ Plants capture light energy from the sun through photosynthesis. This

process takes place in plant cells that have chloroplasts.

◦ Plants take water from the soil and carbon dioxide from the air. In chloroplasts a pigment called chlorophyll absorbs light.

◦ The cell uses the energy to break water into hydrogen and oxygen. The freed hydrogen and the carbon dioxide from the air are combined to make glucose.

◦ Most oxygen from water is released into the air

Cells capture and release energy.

All cells, plant and animal, break down glucose for energy. In cellular respiration, the mitochondria in cells converts small glucose molecules into energy, carbon dioxide, and water. This process is the other half of the energy cycle.

Photosynthesis and cellular respiration are the two processes in the energy cycle.

All cells release energy.

Materials move by diffusion.◦ Diffusion- occurs when molecules spread out until

they are evenly mixed. Molecules move from a higher concentration to a

lower one. Small molecules diffuse through membranes during

passive transport. The diffusion of water through a membrane is called

osmosis.

Materials move across the cell’s membrane.

Cells use chemical energy for active transport. This type of transport is needed for two purposes.

◦ 1. Cells need to move materials from lesser concentrations to greater. Our kidneys use active transport to remove excess salt from our bodies.

◦ Cells need to move large molecules.

◦ Molecules move into the cell through endocytosis and out of it through exocytosis.

◦ In both cases, the cell membrane encloses the molecule in a pocket, pinches off the pocket and removes it.

Some transport requires energy.

Chapter 3- Cell Division!

Let’s take a further look into…

All materials needed by the cell must move across the cell membrane. If the ratio of volume to surface area is too large and the cell doesn’t change shape, there will not be enough membrane area to transport materials into and out of the cell.

Cells therefore undergo the following:◦ 1. staying small◦ 2. dividing◦ 3. changing shape

Cell size affects transport.