Which of the following structures is a tissue

Analyze the question: You are asked to pick the option that is a tissue, not a single cell.

Concept: A tissue is a group of similar (or closely related) cells that work together to perform a particular function. Examples are xylem, phloem, muscle, and connective tissue. Blood is classed as a fluid connective tissue.

Going through the options:

• A. Vessel element: This is a single cell (a component cell of xylem). Many vessel elements joined end to end make a xylem vessel, so one element alone is not a tissue.
• B. Blood: Blood is made of many cell types (red cells, white cells, platelets) suspended in plasma. Together they carry out transport, defence and clotting. It is a fluid connective tissue, so this is correct.
• C. Sieve tube element: This is a single cell of the phloem, so it is not a tissue.
• D. Erythrocyte: This is a red blood cell, a single cell, so it is not a tissue.

Answer: B. Blood.

Exam tip: When you see a question like this, ask yourself: "Is this one cell or a group of cells?" Words ending in "-cyte" (erythrocyte, leucocyte) and "element" (vessel element, sieve tube element) point to individual cells. Words such as blood, xylem, phloem, and muscle point to tissues.