AP BIO FRQ UNIT 1

Water is essential to all living things.

(a) Discuss THREE properties of water.

1. Specific heat/high heat capacity: Heat absorption without temperature change.

2. Adhesion: Attraction to other molecules that are polar or have charge

3. Cohesion: Attraction to other WATER molecules due to polar nature of water/surface tension.

(b) Explain each of the following in terms of the properties of water. You are not limited to the three properties discussed in part (a):

• The ROLE of water as a medium for the metabolic processes of cells

Water is a SOLVENT, as it is involved in the dissociation/ionization of materials.

(b) Explain each of the following in terms of the properties of water. You are not limited to the three properties discussed in part (a):

The ABILITY of water to moderate temperature within living organisms and in organisms' environment

Ice can form from water and act as an insulator for lakes, keeping water in a liquid state.

(b) Explain each of the following in terms of the properties of water. You are not limited to the three properties discussed in part (a):

The MOVEMENT of water from the roots to the leaves of plants

Root pressure, which is driven by osmosis/movement of water into roots, contributes to the movement of water from the roots to the leaves of plants.

The diagram shows water molecules as solid ice at 0ºC and as a liquid at 25ºC .

(a) Describe why hydrogen bonds form between water molecules.

There is an attraction between the slightly negatively charged O atom in one water molecule to one of the slightly positively charged H atoms in another water molecule, creating a weak hydrogen bond between the two. Water molecules are polar, so the O atom is more electronegative than the H atoms, so O pulls the electrons in the H atoms towards itself.

The diagram shows water molecules as solid ice at 0ºC and as a liquid at 25ºC .

(b) Explain why the arrangement of water molecules is different in ice and water.

Water molecules slow down as water cools, which makes the hydrogen bonds between them more stable. Once ice forms, the hydrogen bonds cause the water molecules to spread out. When the temperature is higher, the liquid water molecules are moving faster, are forming constantly, and breaking their hydrogen bond.

(c) To help explain surface tension, use a single water molecule in the template and draw arrows representing the possible locations of hydrogen bonds formed by the molecule. The possible hydrogen bonds formed by a water molecule below the surface are shown.

It looks like this:

O

O O

OO

but a little more spaced together w arrows coming out of the top to the other ones.

(d) The arrangement of the water molecules in ice causes the ice to float. Explain how ice floating on the surface of a body of water affects the water in a way that is beneficial to the organisms in it.

The ice that's floating at the top serves as an insulator for the water underneath, which makes the warm water not as likely to freeze to the bottom of the certain body of water.

The secondary compound cyanide (Figure 1) is a toxic, bitter-tasting chemical that is found in apple seeds. Cyanide in seeds is only released and tasted if the seed is crushed. When animals eat apples, they typically eat the sweet fleshy part of the fruit and spit out the seeds or swallow them whole.

5. Based on the chemical structure of cyanide, identify ONE type of biological macromolecule that could serve as a chemical precursor for the production of cyanide in a plant. Justify your choice.

Identify: Nucleotides or nucleic acids

Justification: Because the macromolecule contains nitrogen.

The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used.

(a) Identify the type of monomer of which this enzyme is composed.

Amino Acids

The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used.

b) Bromelain works by breaking the enzymes that cause browning into smaller molecules. Explain how the reaction that breaks up the enzymes occurs.

by breaking the bond between the amino acids by using water as a reactant.

The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used.

(c) The pH of a solution determines the charge of certain R groups. The pH of pineapple fruit ranges from 3.5 to 5.2. Predict the effect on the activity of bromelain if it is used in a product with a of pH 11.

The activity of bromelain will decrease.

The stems and fruits of pineapple plants contain a group of protein-digesting enzymes collectively called bromelain and often used as an antibrowning agent for fruits and vegetables. Fruits and vegetables brown when they are bruised during transport or sliced and exposed to air. This browning is controlled by enzymatic pathways that produce brown pigments. The browning of fruits and vegetables reduces the nutritional value of the food, so antibrowning agents such as bromelain are used.

(d) Provide reasoning to justify your prediction.

When the pH changes, that will affect the interactions between amino acid R-groups in the enzyme. This will change the folding of the enzyme, which will change its shape and function.