Pakistan MCQs

Motor neurons transmit signals from the nervous system to effectors such as muscles. Damage reduces voluntary or reflex movement.

Internal chemoreceptors can detect gases or pH changes and help regulate breathing and circulation. This supports homeostasis.

Steroid hormones are lipid-soluble and can pass through cell membranes. Their receptor complexes often regulate transcription in the nucleus.

Jointed appendages permit controlled walking and balance in arthropods. Losing a leg disrupts mechanical coordination even if other systems continue working.

Annelids rely on fluid-filled compartments and muscle contractions, whereas arthropods rely on a rigid external cuticle with jointed appendages.

The femur is an internal bone of the vertebrate endoskeleton. Fish scales are external protective structures, not limb bones.

Myelin forms an insulating sheath around many axons and allows faster saltatory conduction. Damage to myelin slows or disrupts nerve signaling.

Hydrostatic skeletons use fluid pressure inside body cavities to support soft tissues. Annelids are a standard example because their coelomic fluid works with muscles during movement.

Many limb movements depend on antagonistic muscle pairs. One muscle shortens while the opposing muscle relaxes, allowing controlled movement in opposite directions.

Vertebrate bone stores calcium salts and phosphate, which give hardness and structural strength. Mineral storage is an additional skeletal function.

Reflex arcs can process information through the spinal cord or local neural circuits, producing rapid protective responses before conscious perception.

Tendons are tough connective tissues that attach muscles to bones. They transmit contractile force so bones move at joints.