Quick questions on Cell Organelles and Function - TCE Biology (Tasmania)

The nucleus is the control centre. It is surrounded by a double membrane (the nuclear envelope) pierced by pores that allow molecules such as mRNA to pass out. Inside, the DNA is stored as chromatin. The nucleus controls the cell by determining which proteins are made, and it contains the nucleolus, where ribosomes are assembled.

Mitochondria are the site of aerobic cellular respiration, releasing energy from glucose and storing it as ATP. Each has a double membrane, with the inner membrane folded into cristae to give a large surface area for the reactions that produce ATP. Cells with high energy demands, such as muscle and kidney cells, contain many mitochondria.

Chloroplasts are found in plant cells and some protists and are the site of photosynthesis. They contain the green pigment chlorophyll, which absorbs light. Internal membranes are arranged in stacks (grana) within a fluid (the stroma), giving a large surface for capturing light. Chloroplasts, like mitochondria, have their own small loop of DNA, evidence that both evolved from once-free-living bacteria.

Ribosomes are the site of protein synthesis, reading mRNA and joining amino acids into chains. They are not membrane-bound. Some float free in the cytoplasm, making proteins for use inside the cell, and others are attached to the endoplasmic reticulum, making proteins for export.

Plant cells have three features animal cells lack: a rigid cellulose cell wall outside the membrane for support and protection, chloroplasts for photosynthesis, and a large permanent central vacuole. Animal cells instead often contain centrioles, which help organise cell division.

Across all organelles, structure matches function. Folded membranes maximise reaction surfaces, the nuclear envelope's pores control what leaves the nucleus, and the membranes of the endoplasmic reticulum and Golgi create channels for moving products. Recognising these links is the key skill: given an organelle's structure, you should be able to predict its role, and the reverse.