Explanation​:
Choice B is correct because incisors are used for biting chunks of food. Choice A is incorrect because tearing is the role of canines. Choices C and D are incorrect because crushing or slicing is the role of the premolars, and grinding is the role of molars.

Explanation​:
Choice C – The statement is false. Phospholipids are a class of lipids which have a hydrophilic “head” and two hydrophobic “tails.” The heads contain a phosphate group and the two tails each contain one fatty acid.

Choice A, B, and D – These statements are all true.

Explanation​:
When two monosaccharides are joined together to form a disaccharide, water is produced, therefore it is a condensation reaction. Choice A is correct.

Choice B is incorrect as hydrolysis uses water to break bonds, in this case converting a disaccharide into a monosaccharides. Choice C is incorrect as catabolism breaks down large molecules into smaller molecules. Choice D is incorrect as oxidation means adding oxygen or losing electrons.

Explanation:
Choice A is correct because a lysosome usually fuses with phagocytic vacuoles containing pathogens or cellular debris, or other vacuoles in the cytoplasm. The enzymes are then released from the lysosome into the vacuole to digest the contents.

Choice B is incorrect because lysosomes contain digestive enzymes that break down cellular components, which involve catabolic reactions, not anabolic reactions. Choice C is incorrect because lysosomes form from vesicles budding off of the Golgi apparatus. Choice D is incorrect because lysosomes are membrane-bound organelles.

Explanation​:
Water is cohesive because it is a polar molecule. The oxygen atom in one water molecule forms a hydrogen bond with the hydrogen atom of another water molecule. In xylem vessels water is attracted to the hydrophilic regions of the cell wall and hydrogen bonds are formed. This an accurate description of the adhesive properties of water in the context of water transport in plants (Choice A). These statements are reversed in Choice D.

Ions dissolve in water, but this is not related to the cohesive (Choice B) or adhesive (Choice C) properties of water.

Explanation​:
Obligate anaerobes are single-celled organisms that will not survive if oxygen is present. Facultative anaerobes are organisms that can either respire aerobically or anaerobically. Obligate aerobes can only respire if oxygen is present and cannot survive in conditions low in oxygen. Therefore Choice A is correct.

Choices B and D are incorrect because obligate anaerobes cannot respire when oxygen is present. Choice C is incorrect as obligate anaerobes require anoxic conditions, and obligate aerobes cannot carry out anaerobic respiration.

Explanation:
The diagram shows glycerol and 3 fatty acids. When these are joined in a condensation reaction, a triglyceride is formed. Choice D is correct.

Choices A, B and C are incorrect.

Explanation​:
Choice B is correct because Rubisco is the name of the enzyme which is responsible for the fixation of carbon during photosynthesis. Choice A is incorrect as rhodopsin is a pigment found in the retina which is responsible for detecting light . Choices C and D are incorrect as neither are enzymes, with collagen being a structural component of tissues such as skin and insulin being a hormone responsible for regulating blood glucose levels.

Explanation​:
The enzyme lactase breaks down the substrate lactose into glucose and galactose.

Glucose and galactose are products of the reaction (Choices A and B).

Fructose is not a substrate for the enzyme lactase (Choice D).

Explanation​:
Choice D is correct because multipotent stem cells can produce only cells of a particular tissue or organ. Choice A is incorrect because pluripotent stem cells are usually found in early embryos and are capable of differentiating to become any cell type found in the organism except for extra-embryonic tissues such as the placenta. Additionally, they are not found in bone marrow. Choice B is incorrect because totipotent stem cells are only found in early stages of embryonic development and can produce all cell types of the organism as well as extra-embryonic tissues such as the placenta. Choice C is incorrect because stem cells are by definition, undifferentiated.

Explanation:
Choice C is correct because the habitat is a place a community, population, species, or organism lives. Choice A refers to an organism's niche, Choice B refers to the ecosystem, and Choice D refers to a community.

Explanation:
Protein pumps are membrane proteins that pump molecules up their concentration gradient using energy in the form of ATP.

Protein channels (Choice A) carry out passive transport while receptors (Choice D) and peripheral proteins (Choice C) do not transport proteins.

Explanation​:
Amino acids (Choice B) can form polypeptides through the formation of peptide bonds as a result of condensation reactions. Fatty acids (Choice A) are involved in the formation of lipids and are not monomers. Proteins (Choice C) are composed of one or more polypeptides and are polymers. Nucleotides (Choice D) are the building blocks of DNA and RNA.

Explanation​:
Statement I
In the Singer-Nicholson model of the plasma membrane, proteins were believed to move within the phospholipid bilayer. The finding that proteins can move throughout the membrane supported the Singer-Nicholson model and refuted earlier models. Statement I is correct.

Statement II
In an earlier model, proteins were assumed to form one layer above and one layer below the phospholipids. The finding that some membrane proteins were hydrophobic (nonpolar) refuted this model and supported the Singer-Nicholson model, since hydrophobic proteins could not form a continuous layer along the charged phospholipid heads but could be embedded within the nonpolar phospholipid tails. Statement II is correct.

Statement III
In an earlier model, the membrane was assumed to consist of three layers (a layer of lipids sandwiched between two layers of proteins). The finding that the membrane consists of two dark bands separated by a light band was consistent with this earlier model. Statement III is incorrect.

Explanation​:
Choice D is correct because starch is made of chains of alpha glucose, proteins are made of chains of amino acids and triglycerides are made of fatty acids and glycerol. Choice A is incorrect because starch is not composed of beta glucose and peptides are not the simplest units of proteins. Choice B is incorrect because starch is not composed of beta glucose and triglycerides do not contain glycogen. Choice C is incorrect because peptides are not the smallest unit of proteins and triglycerides do not contain glycogen.

Explanation:
Choice A is correct because there is no compartmentalisation in prokaryotes, hence transcription and translation both take place in the cytoplasm.

Choice B is incorrect because mRNA splicing does not occur in prokaryotes, but does occur in the nucleus of eukaryotic cells. Choice C and D are incorrect because the regulation of transcription and translation of mRNA into a polypeptide chain occurs in both prokaryotes and eukaryotes.

Explanation​:
The process of air entering the lungs is known as inhalation. The term $\text{“}$inspiration$\text{”}$ is used instead of inhalation sometimes. In order for inhalation to take place, the pressure inside the lungs must be lower compared to atmospheric pressure. To decrease the pressure inside the lungs, the external intercostal muscles must contract and become shorter to pull the ribs up and out, increasing the volume inside the thorax.

Choice A is incorrect because abdominal wall muscles relax during inhalation. Lengthening of the abdominal muscles can contribute to inhalation by pushing the abdominal wall out which increases the volume inside the thorax.

Choice B is incorrect because when the diaphragm relaxes it forms a dome shape and therefore reduces the volume of the thorax. This occurs during exhalation.

Choice D is incorrect because internal intercostal muscles relax and lengthen during inhalation. They contract and shorten during exhalation.

Explanation:
The triglyceride molecule consists of one glycerol molecule and three fatty acids.

A phosphate head and two fatty acid tails (Choice A) form a phospholipid, not a triglyceride. One fatty acid and three glycerol molecules (Choice B) or one glycerol molecule and three monosaccharides (Choice D) cannot form a triglyceride.

Explanation​:
During exhalation, the diaphragm relaxes and lifts upwards to form a dome shape (Statement I). The internal intercostal muscles contract and pull the ribcage inwards and downwards (Statement II).

This causes the volume inside the thorax to decrease which increases pressure inside the thorax (Statement III). Thus the air is forced out of the lungs.

Explanation​:
A potometer is used to measure the rate of transpiration in a plant. When transpiration takes place, water loss occurs because water evaporates inside the leaves and then diffuses out of the leaves. The bubble in the capillary tube will move in the direction of the plant along with the water in the capillary tube which is being absorbed by the plant (Choice C).

Choice B is incorrect because the water and bubble are moving towards the plant, not away from it.

Choice A is incorrect because the water in the reservoir will stay at the same level. The reservoir contains a switch that is used to refill the capillary tube and push the bubble back to the start position. This is done at the end of the experiment to reset the apparatus for the next measurement.

Choice D is incorrect as the water level in the beaker will decrease as water enters the capillary tube and also because of evaporation from the beaker to the atmosphere.

Explanation:
Choice C is correct because Y is the nucleus and is an organelle, whereas X is the cytosol and not an organelle.

Choice A is incorrect because only X, the cytosol, is primarily composed of water and solutes, Y, the nucleus, primarily contains the DNA. Choice B is incorrect because Y, the nucleus, has a specialised function. Choice D is incorrect because Y, the nucleus, is not found in prokaryotes, but both X, the cytosol, and Y, the nucleus, are found in eukaryotes.

Explanation:
The bond formed between two glucose molecules to form maltose is an alpha 1-4 linkage. This is a covalent bond between two alpha glucose molecules, where the carbon #1 of one of the glucose molecules forms a bond with the carbon #4 of the other glucose molecule. Choice C is correct.

A hydrogen bond (Choice A) is a weak electrostatic attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom and another electronegative atom in a different molecule or region of the same molecule. For example, between two water molecules. Peptide bonds (Choice B) are covenant bonds that hold amino acids together in polypeptide chains, and phosphodiester bonds (Choice D) are covalent bonds between the ribose sugars and phosphate groups, forming the backbone of DNA and RNA. Choices A, B and D are incorrect.

Explanation:
Structure X is a peripheral protein that is attached to one surface of the cell membrane.

Protein channels span the width of membranes (Choice B) as do transmembrane proteins (Choice A). Cholesterol molecules do not have a globular structure (Choice D).

Explanation​:
Autotrophs are producers (Choice A, B). They are self-feeding whereas heterotrophs are organisms that gain nutrition by feeding on another organisms (Choice C, D). Detritivores consume dead organic matter by ingestion (Choice C) whereas saprotrophs break down food outside their bodies by secreting enzymes into the environment.

Explanation​:
Ducks and fish are consumers (Choice B, C and D), which is a type of heterotroph, whereas Azolla and rice can carry out photosynthesis and are, therefore, autotrophs (self-feeding).