What Are Cells Made Of? - Eukaryotic Plant Cells (Part 1 of 2)

Good to see you again. Hopefully my last hub series, touring the Eukaryotic Animal cell, has whetted your appetite to take a closer look at a Plant Cell. Take a look at the cell above. It is clear that Animal cells are very similar to Plant cells. This makes sense, as both are classified as Eukaryotes.

If you cast your mind back to my first tour, I explained that GCSE pupils have a misguided view of what constitutes an animal cell. Happily, when asked the question "What is the difference between a Plant and Animal Cell" they are much closer to the mark, tending only to leave out one major difference.

So, pack your camera, take a seat and enjoy our exploration of, perhaps, the most important organisms on the face of the planet.

Plants are producers - they make their own food by combining carbon dioxide and water (and energy from the sun) to make glucose. This neat biochemical trick is called Photosynthesis and is essentially the reverse of Respiration. As we shall see, the series of reactions we collectively call "Photosynthesis" occur entirely in cellular organelles called chloroplasts. These organelles are packed with a pigment called chlorophyll - it is this chemical that absorbs light energy.

Why are plants green? Easy! Chlorophyll is a green molecule.

Why is chlorophyll green? We perceive colours when certain wavelengths of light are reflected from an object and hit cone cells in our eyes. Chlorophyll absorbs red and blue wavelengths of light, but reflect green. Plants that live in shady conditions tend to be dark green because they make extra chlorophyll to try and capture as much light as possible. Plants with pale green leaves tend to live in bright sunshine - they don't need to expend extra energy making more chlorophyll if light is in plentiful supply.

Without plants, there could be no life on Earth.

Plant food is vital to the survival of plants, but it is not 'food' in the traditional sense. We have just established that plants make their own food by photosynthesis. Plant food contains essential micronutrients - typically Potassium, Nitrates and Phosphates. Deficiencies in each of these nutrients result in tell-tale symptoms. Plant food is essentially vitamin tablets for plants.

• Nitrogen - the major component of nucleic acids, amino acids and chlorophyll. The leaves turn yellow when nitrogen-deprived because of a lack of chlorophyll
• Phosphorus - makes up the backbone of RNA and DNA; also used in production of ATP (energy molecule in eukaryotes). Phosphate deprivation causes stunted growth (cells can't make DNA so can't divide their cells so can't grow)
• Potassium - component of proton pumps and vital in protein synthesis. Leaf veins and edges becomes yellowed or purple due to cellular damage and lack of protein

Examining all the organelles present in a typical plant cell is inefficient as the Nucleus, Endoplasmic Reticulum, Golgi, Mitochondria, Peroxisomes, Cell Membrane and Cytoplasm are broadly identical to their Animal counterparts. Instead we will skip over these to focus on the new attractions. Lysosomes, centrioles and one or two other organelles are completely absent from plant cells. If you want more detail or some links, please visit my Animal Cell tour. And now, onward to the Chloroplasts!