Cellular Transport and Biochemistry

Which statement describes all enzymes?

• They control the transport of materials.
• They provide energy for chemical reactions.
• They affect the rate of chemical reactions.
• They absorb oxygen from the environment.

An enzyme and four different molecules are shown in the diagram. The enzyme would most likely affect reactions involving...

• A only

• C only

• B and D

• A and C

Answer explanation

Enzymes work only with specifically shaped substrates.

They have to fit together like a key fits a lock.

Meat tenderizer contains an enzyme that interacts with meat. If meat is coated with tenderizer and then placed in a refrigerator for a short time, how would the enzyme be affected?

• It would be broken down

• Its activity would slow down.

• Its shape would change.

• It would no longer act as an enzyme.

Answer explanation

Enzymes are catalysts that cause change. In this picture, the banana changes from yellow to brown. Putting it in the heat SPEEDS UP the reaction.

In this question, Putting the meat in the cold SLOWS DOWN the reaction.

Hot an cold affect how fast the enzyme works.

The graph shows the results of an action of the enzyme catalase on a piece of meat. Evidence of enzyme activity is indicated by bubbles of oxygen. Which statement best summarizes the activity of the catalase shown in the graph?

• the enzyme works best from 10 C than at 50 C

• the enzyme works better at 5 C than at 65 C

• the enzyme works better at 35 C than at either temperature extreme

• the enzyme works at the same level in all environments

Answer explanation

Temperature affects the how fast an enzyme works.

In the graph the most bubbles were ceated at 35 C. On the left and right of the graph, the number of bubbles is very low.

* 'the extremes' means the highest and lowest temperatures.

Substances X and Y are examples of which kind of molecule?

• simple sugar

• amino acid

• fat

• hormone

Answer explanation

The starch molecule breaks down into sugar (glucose).

Protein molecules break down into amino acids.

Fat breaks down into smaller fatty acids or glycerol.

Which way is the water moving in this cell?

• Water will move out of the cell
• Water will move into the cell

Answer explanation

Water will naturally want to move from HIGH concentration to LOW concentration through Osmosis.

Look closely at in the picture to find where there is more water and where there is less water.

Osmosis is the movement of _____ across a membrane.

• food

• oxygen

• lipids

• water

Answer explanation

Osmosis is always connected to the movement of WATER.

This cell organelle helps organisms maintain homeostasis by controlling what substances may enter or leave cells.

• vacuole

• cell membrane

• cell wall

• nucleus

Answer explanation

The cell membrane is semipermeable and allows molecules to enter and exit using diffusion, osmosis and active transport.

When most proteins, fats, and carbohydrates are digested completely, they are converted to end products that

• are soluble and can easily pass through cell membranes

• contain long chains of amino acids and fat acids

• contain atoms of carbon, hydrogen, oxygen, and nitrogen

• are a direct result of dehydration synthesis

Answer explanation

Digestion breaks molecules apart into smaller pieces. Those smaller pieces can pass through the cell membrane much easier than larger macro-molecules.

A biologist observed a plant cell in a drop of water as shown in diagram A. The biologist added a 10% salt solution to the slide and observed the cell as shown in diagram B.

The change in appearance of the cell resulted from

• more salt moving out of the cell than into the cell

• more salt moving into the cell than out of the cell

• more water moving into the cell than out of the cell

• more water moving out of the cell than into the cell

Answer explanation

Water wants to move from HIGH concentration to LOW concentration.

If there is less water outside the cell, water will move OUT of the cell and into the hypertonic solution.

Adding salt to the solution will draw water OUT of the cell.