Most Repeated MDCAT Biology: Transport MCQs

Explanation

Red blood cells are involved in the transport of O2 via haemoglobin stored in them from the lungs to the cells and tissues of the body. Option A, B and C are wrong as they are the physical barriers (part of 1st line of defense) that protect our body from germs. Option D is wrong as white blood cells are the main cells that fight with the pathogens entering our body.

Explanation

The system that is responsible for fighting the pathogens in the human body is called the immune system. The endocrine system deals with all the hormones, nervous system deals with nerve impulses coming to the human body and its responses to these stimuli. The muscular system deals with movement.

Explanation

This is the correct answer. The apoplast pathway is the movement of water through the cell walls and intercellular spaces of plant tissues. In roots, the apoplast pathway is disrupted by the endodermis, a layer of cells that surrounds the vascular bundle. The endodermal cells have a specialized structure called the Casparian strip, which is a waterproof band that seals the cell walls, preventing water from moving freely through the apoplast. This forces water to enter the symplast pathway, passing through the cytoplasm of endodermal cells and then into the xylem.

Explanation

The tricuspid valve is one of the heart's atrioventricular valves, situated between the right atrium and the right ventricle. Its primary function is to prevent the backflow of blood from the right ventricle into the right atrium when the ventricle contracts. This distinguishes it from other valves like the mitral valve on the left side, which prevents backflow from the left ventricle into the left atrium, the aortic valve, which prevents backflow into the left ventricle from the aorta, and the pulmonary valve, which prevents backflow into the right ventricle from the pulmonary artery. Therefore, option D is the correct answer, as it accurately describes the function of the tricuspid valve.

Explanation

Mucous membranes are a type of epithelial tissue that lines the inside of many organs, including the respiratory tract, digestive tract, and genitourinary tract. They are part of the body's first line of defense against infection, and they offer physical barriers in several ways: The mucus layer: Mucus is a thick, sticky substance that is produced by the cells of the mucous membrane. It helps to trap bacteria and viruses, preventing them from reaching the underlying tissues. The tight junctions: The cells of the mucous membrane are held together by tight junctions, which are small gaps between the cells.

Explanation

The right atrium is separated from the right ventricle by the tricuspid valve. The tricuspid valve is a three-leaflet valve that allows blood to flow from the right atrium to the right ventricle. The tricuspid valve is located at the opening of the right ventricle. The tricuspid valve is made up of three leaflets, which are called the septal leaflet, the anterior leaflet, and the posterior leaflet. The leaflets are attached to the papillary muscles by chordae tendineae. The papillary muscles are attached to the walls of the right ventricle.

Explanation

The valve lying between the right atrium and the right ventricle is known as the tricuspid valve due to it having three flaps.

Explanation

The variable regions of an antibody are responsible for antigen recognition and binding. Antibodies are the soluble proteins produced in response to an antigen by the B-cells. They are Y-shaped molecules consisting of four polypeptide chains: two identical heavy chains and two identical light chains. The two ends or tips of the Y-shaped molecule of an antibody are the variable regions, which are the parts of the antibody that combines with the antigen. The variable regions of a particular antibody can only join with a particular antigen.

Explanation

In a vascular cambium, the xylem is placed on the inner side while the phloem is placed on the outer side, option B states the opposite.

Explanation

Cyanosis occurs when oxygen-depleted (deoxygenated) blood, which is bluish rather than red, circulates through the skin. This occurs when there is the mixing of blood which takes place when there is a septal defect in the heart, e.g Ventricular Septal Defect (VSD).

Explanation

Atherosclerosis is a disease caused by high levels of cholesterol in the blood. The immune system comprises of cells such as lymphocytes, neutrophils, eosinophils, basophils, and phagocytes such as macrophages. It also has complement proteins that help in combatting the incoming pathogen. Cytokines released act to promote an immune response to the pathogen in the form of inflammation.

Explanation

his is the correct statement. The semilunar valves are located at the base of the aorta (aortic valve) and the pulmonary artery (pulmonary valve). These valves prevent the backflow of blood into the ventricles after it has been pumped out of the heart. When the ventricles relax, the semilunar valves close, ensuring that blood does not flow backward from the arteries into the heart.

Explanation

This is the correct answer. Facilitated diffusion is a type of passive transport that allows specific molecules, such as ions and large molecules, to move across the cell membrane from a region of higher concentration to a region of lower concentration with the aid of membrane proteins. These proteins act as channels or carriers, allowing the molecules to pass through the membrane more efficiently than they would be able to do on their own.Therefore, the movement of ions and large molecules with the help of protein molecules is called facilitated diffusion.

Explanation

Modern research shows stomatal opening is driven by ion movements in guard cells. Potassium ions enter guard cells, lowering water potential and causing water uptake. This increases turgor in guard cells, opening the stomata.

Explanation

Facilitated transport is a passive process that moves molecules down their concentration gradient with the help of specific membrane proteins. Option B, 'Uphill transport,' is incorrect for facilitated transport because it involves moving substances against their gradient, requiring energy input, which is characteristic of active transport. Option A, 'Transport saturation,' is a valid feature of facilitated transport as it reaches a maximum rate when all proteins are occupied. Option C, 'Requirement of special membrane proteins,' is true since facilitated transport depends on specific proteins to move molecules.

Explanation

Haemoglobin consists of four polypeptide chains. Each chain is associated with a haem group. Haeme group is an iron-containing group, which consists of porphyrin with a central atom of ferrous (iron) between four pyrrole rings.

Explanation

Guard cells are pairs of specialized epidermal cells that work to control excessive water loss, closing on hot, dry, or windy days and opening when conditions are more favorable for gas exchange. The inner wall of a guard cell is thicker than the outer wall. When the guard cell is filled with water and it becomes turgid, the outer wall balloons outward, drawing the inner wall with it and causing the stomata to enlarge. The outer wall of guard cells is thin and elastic.

Explanation

Chordae tendineae (or simply chordae) are fibrous cords or tendons that are present in the heart to anchor the atrioventricular (AV) valves (specifically, the tricuspid and bicuspid/mitral valves) to the papillary muscles located in the ventricles. This prevents the valves from inverting into the atria when the ventricles contract and helps in maintaining proper valve function.