Which of the following is a fluid connective tissue?

The correct answer is B, Robert Hooke. In 1665 he cut a thin slice of cork, examined it under a microscope of his own making and saw rows of empty boxes, which he named cells after the small rooms of a monastery; the drawing and description appeared in his book Micrographia. Option A is wrong because Robert Brown discovered the nucleus in 1831, more than a century and a half later, and is also remembered for Brownian motion. Option C is wrong because Theodor Schwann, with Matthias Schleiden, proposed the cell theory, that all plants and animals are made of cells; he did not discover the cell itself. Option D is wrong because Anton van Leeuwenhoek was the first to see living cells such as bacteria and protozoa in pond water, but Hooke's observation came first and gave the structure its name. Note that what Hooke actually saw were dead cell walls, since cork is dead tissue.

The correct answer is B, mitochondria and plastids. Both carry a small circular DNA of their own and their own 70S ribosomes, so they make a part of their protein themselves and divide independently of the cell; this semi-autonomous nature is the main evidence for the view that they descend from free-living bacteria engulfed by an early cell. Option A is wrong because the Golgi body and the endoplasmic reticulum are membrane systems that modify and transport material and carry no genetic matter of their own; the rough endoplasmic reticulum merely holds ribosomes on its outer surface. Option C is wrong because the lysosome is only a sac of digestive enzymes and the Golgi body, as stated, has no DNA. Option D is wrong because the vacuole is a storage sac bounded by the tonoplast and has no DNA, even though its partner in the option, the plastid, does. Remember the pair as the two power organelles of the cell.

The correct answer is B, lysosome. A lysosome is a membrane-bound sac of powerful digestive enzymes that breaks down worn-out organelles and any foreign particle the cell takes in; if the cell is damaged or starving, the sacs burst and the same enzymes digest the cell itself, which is why the name suicide bag is used. Option A is wrong because the ribosome is the site of protein synthesis and is called the protein factory of the cell. Option C is wrong because the centrosome, present in animal cells, organises the spindle fibres during cell division. Option D is wrong because the vacuole stores water, sap and waste and keeps a plant cell turgid, which is a storage function and not a destructive one. Two more nicknames belong with this set and are asked just as often: the mitochondrion is the powerhouse of the cell and the Golgi apparatus is its packaging and dispatch unit.

The correct answer is A, Schleiden and Schwann. Matthias Schleiden, a botanist, concluded that all plants are made of cells, and Theodor Schwann, a zoologist, reached the same conclusion for animals; together their statement became the cell theory. Option B is wrong because Robert Hooke only discovered and named the cell and Robert Brown discovered the nucleus, and neither framed a general theory. Option C is wrong because Charles Darwin is associated with natural selection and the origin of species while Gregor Mendel founded the science of heredity through his work on pea plants. Option D is wrong because James Watson and Francis Crick described the double helix structure of DNA in 1953, which belongs to molecular biology. One addition completes the theory and is often the second half of the question: Rudolf Virchow stated that every cell arises from a pre-existing cell, which ruled out the idea of cells forming on their own.

The correct answer is C, tendon. A tendon is made of dense white fibrous connective tissue with great tensile strength and almost no elasticity, so when a muscle contracts the whole pull is transmitted to the bone without being lost in stretching. Option A is wrong because a ligament joins one bone to another across a joint; it contains elastic fibre, stretches to a degree and holds the bones in position, and this is the pair examiners most often interchange. Option B is wrong because cartilage is a soft, flexible supporting tissue found at the ends of bones, in the nose, the ear and the windpipe, where it gives shape and cushions movement. Option D is wrong because areolar tissue is a loose packing tissue that fills the space between organs and under the skin and helps in repair. Fix the pair by the words themselves: tendon for muscle to bone, ligament for bone to bone.