Milk Biosynthesis and Composition Practice Quiz (17 questions)

1. What typically happens to lactase production in most mammals after weaning?

A. It increases, improving the ability to digest lactose.

B. It remains steady, preserving the ability to digest lactose.

C. It decreases, reducing the ability to digest lactose.

D. It shifts to the intestine, leaving lactose digestion unchanged.

Answer: (C)

Explanation

In most mammals, lactase production declines after weaning, which reduces their ability to digest lactose. Continued lactase production into adulthood is the contrasting pattern called lactase persistence.

2. What allows some human populations to continue producing lactase into adulthood?

A. Genetic mutations that support continued lactase production.

B. Fermentation of milk that changes inherited lactase production.

C. A longer childhood period that delays all digestive changes.

D. A higher-fat diet that prevents lactase production from declining.

Answer: (A)

Explanation

Some human populations carry genetic mutations that allow lactase production to continue into adulthood. Fermenting milk can affect the food but does not account for the inherited production pattern described here.

3. How did fermented milks such as piimä and viili contribute to dairy use historically?

A. They made fresh milk available during every season.

B. They increased milk's calcium content and reduced its fat.

C. They helped preserve milk and improve its safety.

D. They replaced milk as a source of calories and protein.

Answer: (C)

Explanation

Fermented milks helped preserve milk and improve its safety, while dairy also supplied calories, protein, and fat. Their historical role was not to increase milk's calcium content.

4. Which group of nutrients and minerals is found in milk?

A. Calcium, phosphorus, high-quality protein, B2 and B12, iodine, and potassium.

B. Calcium, phosphorus, high-quality protein, C and D, selenium, and potassium.

C. Calcium, iron, high-quality protein, B1 and B6, iodine, and sodium.

D. Phosphorus, magnesium, high-quality protein, B2 and B12, zinc, and potassium.

Answer: (A)

Explanation

Milk contains calcium, phosphorus, high-quality protein, vitamins B2 and B12, iodine, and potassium. The other combinations substitute nutrients not included in this stated list.

5. Which sequence describes a dairy cow's breeding, gestation, and milk-production timeline?

A. Bred at 9–10 months, gestates about 15–18 months, and produces milk about 10 months after calving.

B. Bred at 15–18 months, gestates about 10 months, and produces milk about 9–10 months before calving.

C. Bred at 15–18 months, gestates about 9–10 months, and produces milk about 10 months after calving.

D. Bred at 10 months, gestates about 9–10 months, and produces milk about 15–18 months after calving.

Answer: (C)

Explanation

The stated timeline is breeding at 15–18 months, gestation of about 9–10 months, and milk production for about 10 months after calving. A non-lactating period before the next calving is a separate part of the cycle, not the milk-production period.

6. A dairy cow's milk yield and composition change over time and between animals; which factors help explain this variation?

A. Genetics, diet, and stage of lactation.

B. Breed, non-lactating period, and productive lifespan.

C. Calving season, housing, and milking schedule.

D. Age at breeding, gestation length, and herd size.

Answer: (A)

Explanation

Milk composition and production vary with genetics, diet, and the stage of lactation. The cow's breeding age and gestation length describe reproductive timing, rather than the listed sources of milk variation.

7. How is the bovine udder anatomically organized into mammary glands and quarters?

A. It consists of two mammary glands, each divided into two udder quarters.

B. It consists of four mammary glands, each corresponding to one udder quarter.

C. It consists of four udder halves, each containing one mammary gland.

D. It consists of two mammary glands, each corresponding to one udder half.

Answer: (B)

Explanation

The bovine udder has four mammary glands, and each gland corresponds to one quarter. The two-half arrangement describes how the udder is divided, not the number of mammary glands.

8. What does the fine membrane within the bovine udder separate?

A. It separates each udder quarter into two individual mammary glands.

B. It separates the udder into two quarters, each containing two halves.

C. It separates the udder into four halves, each containing one quarter.

D. It separates the udder into two halves, each containing two quarters.

Answer: (D)

Explanation

The fine membrane divides the udder into two halves, with two quarters in each half. The four quarters are individual mammary glands, not subdivisions created by this membrane.

9. Which set lists the routes mammary epithelial cells use to secrete milk components during lactation?

A. Exocytosis, fat secretion, vesicular transcytosis, transporter-mediated movement, and the paracellular pathway.

B. Exocytosis, fat secretion, direct diffusion, transporter-mediated movement, and the paracellular pathway.

C. Exocytosis, fat secretion, vesicular transcytosis, blood filtration, and the paracellular pathway.

D. Exocytosis, fat secretion, vesicular transcytosis, transporter-mediated movement, and intracellular storage.

Answer: (A)

Explanation

Milk components are secreted through exocytosis, fat secretion, vesicular transcytosis, transporter-mediated movement, and the paracellular pathway. Intracellular storage is not one of the listed secretion routes.

10. Which description correctly identifies three major mammary epithelial-cell secretion routes?

A. A cytoplasmic lipid droplet route, a microlipid droplet route, and a secretory route for casein components.

B. A cytoplasmic lipid droplet route, a vesicular transcytosis route, and a secretory route for skim-milk components.

C. A cytoplasmic lipid droplet route, a microlipid droplet route, and a transporter route for skim-milk components.

D. A cytoplasmic lipid droplet route, a microlipid droplet route, and a secretory route for skim-milk components.

Answer: (D)

Explanation

The three major routes include cytoplasmic lipid droplets, microlipid droplets, and a secretory pathway for skim-milk components. The casein-focused pathway is not the specified third route.

11. Which lipid classes make up most milk lipids?

A. Phospholipids and whey proteins.

B. Cholesterol and phospholipids.

C. Triglycerides and caseins.

D. Triglycerides and phospholipids.

Answer: (D)

Explanation

Milk lipids consist mainly of triglycerides and phospholipids. Caseins are milk proteins, so they do not belong in the main lipid classes.

12. Which group contains the four main casein subgroups in milk?

A. αs2-casein, κ-casein, β-casein, and whey globulin.

B. αs1-casein, αs2-casein, γ-casein, and β-casein.

C. αs1-casein, κ-casein, β-casein, and whey albumin.

D. αs1-casein, αs2-casein, κ-casein, and β-casein.

Answer: (D)

Explanation

The four main casein subgroups are αs1-casein, αs2-casein, κ-casein, and β-casein. Whey proteins such as albumin and globulin are a separate category from the casein subgroups.

13. Which description correctly identifies lactose and its component sugars?

A. A milk disaccharide composed of glucose and fructose

B. A milk monosaccharide formed from two glucose units

C. A milk polysaccharide built from galactose units

D. A milk disaccharide composed of glucose and galactose

Answer: (D)

Explanation

Lactose is a milk sugar made of the two monosaccharides glucose and galactose. Glucose and galactose are its components, not the name of a different two-sugar combination such as glucose and fructose.

14. A milk sample is being checked for whether its lactose content falls within the stated range; which interval applies?

A. 1.5% to 3.0%

B. 3.6% to 5.5%

C. 5.8% to 7.2%

D. 8.0% to 10.5%

Answer: (B)

Explanation

Lactose content in milk varies from 3.6% to 5.5%. The higher ranges may sound plausible for a milk component, but they do not match the stated lactose interval.

15. Which sequence correctly describes lactose biosynthesis in a mammary cell?

A. Glucose enters through GLUT1, becomes UDP-galactose in the Golgi, and is transported to the cytoplasm for lactose formation by the same complex.

B. Glucose enters through GLUT1, becomes UDP-galactose in the cytoplasm, and is transported into the Golgi for lactose formation by the lactalbumin–β4-galactosyl transferase complex.

C. Glucose enters through GLUT1 and is converted directly to lactose in the cytoplasm before UDP-galactose is transported into the Golgi.

D. Galactose enters through GLUT1, becomes UDP-glucose in the cytoplasm, and is transported into the Golgi for lactose formation by the same complex.

Answer: (B)

Explanation

The pathway converts incoming glucose to UDP-galactose in the cytoplasm, transports UDP-galactose into the Golgi, and forms lactose there through the specified complex. The similar sequence placing UDP-galactose production in the Golgi reverses the locations of two steps.

16. Which description best characterizes milk exosomes?

A. Small extracellular vesicles, about 30–150 nm, containing proteins, lipids, and RNAs such as microRNAs

B. Small intracellular organelles, about 30–150 nm, made mainly of proteins and lacking nucleic acids

C. Small extracellular vesicles, about 30–150 nm, composed of microRNAs rather than carrying them

D. Large extracellular vesicles, about 300–1,500 nm, containing proteins, lipids, and carbohydrates

Answer: (A)

Explanation

Milk exosomes are extracellular vesicles measuring 30–150 nm and carry proteins, lipids, and RNAs, including microRNAs. They are vesicles that contain these molecules, rather than being intracellular organelles or consisting solely of microRNAs.

17. What is the current state of evidence about the effects of milk exosomes on human health?

A. Evidence comes mainly from in vitro and animal studies, so human health effects remain incompletely established.

B. Evidence comes mainly from cell studies, which have ruled out effects in living organisms.

C. Evidence comes mainly from animal studies, which have established the same effects in humans.

D. Evidence comes mainly from large human trials, which have established broad health benefits.

Answer: (A)

Explanation

Research on milk-exosome effects is mainly based on in vitro and animal studies, and their effects on human health are not fully established. Animal findings alone do not establish that the same effects occur in humans.