Cell – Structure And Function

Chloroplast

Step 1: Compare plant and animal cells. Step 2: Chloroplasts are found only in green plant cells. They are the site of photosynthesis and contain the green pigment chlorophyll. Step 3: Mitochondria are present in BOTH plant and animal cells for respiration. Step 4: Ribosomes are present in ALL living cells (both prokaryotic and eukaryotic). Step 5: Centrioles are present in animal cells but ABSENT in most plant cells. Therefore, chloroplast is the structure unique to plant cells among the given options.

Osmosis

Step 1: Recall the different types of transport across the cell membrane. Step 2: Osmosis specifically refers to the movement of WATER molecules from a region of higher water concentration to lower water concentration through a semipermeable membrane. Step 3: Diffusion is the movement of any molecule from higher to lower concentration, but it does NOT require a semipermeable membrane. Step 4: Active transport moves molecules AGAINST the concentration gradient and requires energy (ATP). Step 5: Endocytosis is bulk intake of large particles. So the correct answer is Osmosis.

Contain enzymes that can digest the cell's own material when damaged.

Step 1: Lysosomes are membrane-bound organelles containing about 40 digestive (hydrolytic) enzymes. Step 2: Under normal conditions, these enzymes digest food, germs, and damaged cell material. Step 3: However, when a cell is old, diseased, or injured, the lysosomal membrane ruptures and the enzymes are released into the cytoplasm. Step 4: These enzymes then digest the cell's own organelles and contents — effectively 'killing' the cell from within. Step 5: This self-destructive ability earns lysosomes the nickname 'suicidal bags'.

70S

Step 1: Ribosomes are classified by their sedimentation coefficient, measured in Svedberg units (S). Step 2: Prokaryotic cells (like bacteria) have smaller 70S ribosomes. Step 3: Eukaryotic cells (like plant and animal cells) have larger 80S ribosomes. Step 4: The S value refers to how fast the ribosome sediments in an ultracentrifuge — higher S means larger and heavier. Step 5: This difference is important in medicine — many antibiotics target the 70S ribosome of bacteria without harming the 80S ribosomes of human cells.