Specialised Plant, Blood, Reproductive and Nerve Cells

Revision notes

Plant cells adapted to transport and photosynthesis

Palisade mesophyll cells are elongated, closely packed beneath the upper leaf surface and contain many chloroplasts. Their position and organelle content support light absorption and photosynthesis. A large vacuole leaves a thin peripheral layer of cytoplasm, helping shorten diffusion paths.

Root hair cells have a long extension increasing surface area for water and mineral-ion uptake. A thin wall gives a short path; membrane transport proteins support selective ion uptake, including active transport. Mitochondria supply ATP. Water enters according to water-potential gradients; root hairs do not actively pump water itself.

Mature xylem vessel elements are dead, hollow and joined end to end, with end walls lost or perforated. Lignified walls resist collapse under tension and provide support. Pits permit lateral water movement. They carry water and mineral ions. Phloem sieve tube elements are living but lack a nucleus at maturity. Sieve plates allow sap flow. Companion cells have nuclei and many mitochondria, supporting loading and maintenance. Phloem translocates assimilates from sources to sinks; different tubes may carry material in opposite directions.

Reproduction

Sperm cells have a haploid nucleus, a flagellum for movement, mitochondria to support ATP supply and an acrosome containing enzymes involved in penetrating egg coverings. An egg cell also has a haploid nucleus; it is much larger, with cytoplasm and reserves supporting early development. Its membrane changes after fertilisation to help prevent polyspermy. Haploid gametes restore the diploid chromosome number when their nuclei fuse.

Blood cells and fragments

Mammalian erythrocytes have a biconcave shape, providing high surface area and a short diffusion distance. They contain haemoglobin and lack nuclei and mitochondria when mature, maximising space and avoiding consumption of transported oxygen by aerobic respiration. Their flexibility permits passage through capillaries.

Leucocytes have nuclei and defend the body. Phagocytes engulf pathogens; lymphocytes include cells producing antibodies and cells participating in other immune responses. Do not assign antibody secretion to every white cell. Thrombocytes, or platelets in mammals, are fragments derived from megakaryocytes. They adhere at damaged vessels and contribute to clot formation; they are not complete nucleated human cells.

Neurones

Neurones receive and transmit electrical signals. Dendrites receive inputs, the cell body maintains the cell, and a long axon carries impulses towards terminals. Myelin insulates many axons and nodes permit rapid saltatory conduction. Synaptic terminals communicate with other cells through neurotransmitters. The exact shape varies with sensory, relay and motor roles.

Worked application and data skills

A cell in a plant transport tube has no nucleus but is still living and lies beside a mitochondria-rich companion cell. Identify a phloem sieve tube element, not a xylem vessel. A mature xylem vessel element is dead and has lignified walls. In a blood film, a biconcave cell without a nucleus suggests an erythrocyte; a nucleated cell is more consistent with a leucocyte.

Common misconceptions

Platelets are cell fragments in humans. Mature phloem sieve tubes are living despite lacking a nucleus. Root hairs actively transport ions, not water.

Examination tips

Always write adaptation → effect → function. Include every named cell group in your revision.

Check your understanding

Five original questions. Use Tab to move between controls, arrow keys within a radio group, and Enter or Space on buttons. Feedback appears after Check Answer. Try Again clears the question. Attempts are not saved.

Sources and scope

Scope: Unit 1 A2.1. Original BTECRevision notes, schematics and questions. Independent resource; not endorsed by Pearson.

Official Pearson specification. Scientific review references are listed in the accompanying QA report.