Cell level systems Study Guide

Cells are the fundamental units of life, and their ability to carry out various processes depends on the specialized structures within them. These structures, known as sub-cellular components or organelles, each perform specific functions essential for the cell's survival. Eukaryotic cells, found in plants, animals, fungi, and protists, are characterised by having a true nucleus and other membrane-bound organelles. Animal and plant cells are both eukaryotic but have some key differences in their sub-cellular structures that relate to their unique modes of life. For instance, plant cells possess a cell wall for structural support, chloroplasts for photosynthesis, and a large permanent vacuole for maintaining turgor, none of which are found in animal cells. Both animal and plant cells share common structures like the nucleus (controlling cell activities), cytoplasm (where chemical reactions occur), cell membrane (controlling substance movement), mitochondria (site of aerobic respiration and energy release), and ribosomes (site of protein synthesis). In contrast, prokaryotic cells, found in bacteria and archaea, are simpler and smaller. They lack a nucleus and other membrane-bound organelles. Their genetic material is a single DNA loop in the cytoplasm, often accompanied by smaller rings of DNA called plasmids. Prokaryotic cells also have a cell membrane, cytoplasm, and ribosomes, similar to eukaryotes, but their cell wall is made of peptidoglycan, not cellulose as in plants. Some prokaryotes also have a flagellum for movement. Understanding these structural differences and their corresponding functions is crucial for comprehending how different cell types are adapted to their roles in living organisms.

Sugars are fundamental biological molecules that serve as the basic building blocks (monomers) for all carbohydrates. The most common monosaccharide is glucose, a simple sugar that plants produce during photosynthesis. Organisms then use glucose in two main ways: for energy release through respiration, or as a monomer to construct larger carbohydrates. During respiration, glucose is broken down to release energy for cellular activities. This is a vital process for all living cells. Conversely, organisms can link many glucose molecules together through chemical reactions to synthesize larger, more complex carbohydrate polymers, such as starch in plants or glycogen in animals. These complex carbohydrates act as energy storage molecules or provide structural support, such as cellulose in plant cell walls. The process of linking these sugar units together is called polymerisation, and the reverse process, breaking them down into simpler sugars, is hydrolysis. Enzymes catalyse both these synthesis and breakdown reactions, ensuring they occur efficiently at biological temperatures. Therefore, sugars are crucial because they form the foundational units for constructing all other carbohydrates and are also the primary molecules cells break down to obtain energy, making them central to metabolism.