All Free Biology MCQs with Answers

1001. __________ arranges the DNA into the chromosomes in a eukaryotic cell.

• A. Hormones
• B. Elastin
• C. Histone
• D. Nucleosome

Explanation: Histones are small positively charged proteins that the negatively charged DNA winds around, condensing roughly two metres of DNA into a nucleus a few micrometres across. A nucleosome is the resulting bead of DNA wrapped around eight histones, so it is the product of the packaging rather than the agent doing it, which makes it the deliberate near miss here. Elastin is a structural protein of connective tissue.

1002. The function of nucleolus is to make:

• A. rDNA
• B. Lysosomes
• C. Ribosomes
• D. Chromosomes

Explanation: The nucleolus transcribes ribosomal RNA and assembles it with proteins into the ribosomal subunits, which are then exported through the nuclear pores. Cells that make a great deal of protein have correspondingly prominent nucleoli. Lysosomes are budded off by the Golgi apparatus, and rDNA is the template the nucleolus reads rather than something it makes.

1003. Which of the following blood vessels have lowest blood velocity with correct reason for low blood velocity?

• A. Arteries: Due to thick walls
• B. Capillaries: due to highest overall cross-sectional area
• C. Veins: due to blood flow against the gravity
• D. Capillaries: Due to two-way blood flow in capillaries

Explanation: Although each capillary is tiny, there are so many in parallel that their combined cross sectional area is far greater than that of the aorta, and since the same volume must pass every second, the velocity falls to about a millimetre per second. That slow flow is exactly what exchange requires, giving time for diffusion. The fourth option names the right vessel but an invented reason, since capillary flow is one way.

1004. An active athlete has more stamina of running compared to an officer of same age with physically inactive lifestyle. Which of the following organelles has greatly increased in the muscle cells of athlete?

• A. Nucleus
• B. Mitochondria
• C. Golgi bodies
• D. Smooth endoplasmic reticulum (SER)

Explanation: Endurance training increases the number and size of mitochondria in muscle fibres, so more ATP can be produced aerobically and the athlete relies less on anaerobic respiration and accumulates lactate more slowly. This is one of the main measurable adaptations to training. The number of nuclei and the extent of the Golgi are not what limits stamina.

1005. Once an action potential reaches the membrane of a skeletal muscle fiber, what is the first event that occurs in the contraction process?

• A. Actin and myosin form a cross-bridge
• B. Calcium is pumped back into the sarcoplasmic reticulum
• C. Calcium is released from the sarcoplasmic reticulum
• D. ATP is hydrolyzed by troponin

Explanation: The action potential travels down the T tubules and triggers the sarcoplasmic reticulum to release calcium, which then binds troponin and moves tropomyosin off the binding sites so cross bridges can form. Cross bridge formation therefore comes second, not first, which is the trap in the first option. Pumping calcium back is what ends the contraction.

1006. The pubic symphysis is a slightly moveable joint joined by which of the following tissue?

• A. Elastic cartilage
• B. Fibrocartilage
• C. Costal cartilage
• D. Articular cartilage

Explanation: Fibrocartilage is tough and compressible, which suits a slightly movable joint that must bear load, and it is the same tissue found in the intervertebral discs and the menisci of the knee. Articular cartilage is the smooth hyaline layer covering bone ends in freely movable joints. Elastic cartilage supports the pinna of the ear and costal cartilage joins the ribs to the sternum.

1007. In a pea plant seed color is determined by two alleles: Y (Yellow, dominant) and y (green, recessive). Which parental cross would most likely result in offspring showing a 1:1 ratio of yellow to green seeds?

• A. Yy x YY
• B. Yy x yy
• C. Yy x Yy
• D. YY x yy

Explanation: Crossing a heterozygote with a homozygous recessive gives half Yy and half yy, that is one yellow to one green, which is the classic test cross. Yy by Yy gives three yellow to one green, and any cross involving YY gives all yellow because every offspring receives at least one dominant allele. Recognising the test cross by its 1:1 outcome is the quickest route.

1008. Mendel crossed a plant with round yellow seeds (RRYY) and a plant with wrinkled green seeds (rryy), what was the phenotype of all F1 offspring?

• A. All round green
• B. All round yellow
• C. All wrinkled yellow
• D. All wrinkled green

Explanation: Every offspring receives R and Y from one parent and r and y from the other, so all are RrYy and both dominant characters show, giving round yellow seeds. The recessive wrinkled and green phenotypes reappear only in the F2, in the familiar 9:3:3:1 ratio. This uniform F1 is what Mendel's law of dominance describes.

1009. In a normal 28 days menstrual cycle when would you expect the LH surge to occur?

• A. Days 7-10
• B. Days 11-14
• C. Days 15-18
• D. Days 19-22

Explanation: Ovulation falls at about day 14, and the LH surge precedes it by roughly a day, so it lies in the window from day 11 to 14. The luteal phase after ovulation is the fixed part of the cycle at about fourteen days, which is why counting back from the next expected period is the reliable method. Days 15 to 22 fall after ovulation, when progesterone dominates.

1010. Which property of water helps in moderating Earth's climate and maintaining stable temperature in aquatic environment?

• A. Low viscosity
• B. High specific heat capacity
• C. High surface tension
• D. High polarity

Explanation: A great deal of energy goes into breaking hydrogen bonds before the temperature of water rises, so oceans and lakes absorb and release heat with only small temperature changes and coastal climates stay mild. Polarity is the underlying cause of the hydrogen bonding, but the property that directly buffers temperature is the specific heat capacity. Surface tension matters for insects walking on water rather than for climate.