A Brief Encounter with Plant Components

Ahh the different parts of the plant. Aren’t they amazing?!

1. Roots

Hello everyone! Plantastic Science is establishing its roots on the Internet. So, there really seems no better place to start than the roots of plants! Roots of plants are specialised. What this means is different types of roots look different and behave differently in order to perform a certain task or duty better. For example, on a soccer team the attacker, defender and goalie all have different skill sets and strengths. Together as a team they can ensure success! The same applies all organs within a plant, as they work together to maximize its chances of survival and within the root ‘sub-team’ if you will.

There are two main types of roots we are going to be looking at today. They are called the primary roots and lateral roots. The primary roots grow downward and anchor the plant, stabilizing it in the soil. The last thing a plant would want is to be blown straight out of the soil with a light breeze! Lateral roots, on the other hand, branch off from the primary root and increase the surface available for nutrient and water absorption. Lateral roots have adapted to their function by having tiny extensions from their epidermal cells, called root hairs. These elongated protrusions increase the root’s capacity to absorb water and minerals by osmosis and diffusion as increased surface area increases the rate of these processes.

Roots are also known as storage organs. They store carbohydrates most commonly in the form of starch inside organelles called amyloplasts. Starch is a polysaccharide consisting of many glucose units and is commonly tested for with iodine, a biomolecule test you may very well have conducted in school. If any biological sample is tested with iodine, and a blue-black colour appears, you know the fabulous starch is present!

Did you know?: In legumes, plant roots form symbiotic relationships with nitrogen-fixing bacteria to enrich soil fertility. A symbiotic relationship is one where both organisms involved benefit off of each other. In legumes, the bacteria receive protection from harmful environmental conditions by being enclosed in root nodules, and legume plants benefit from the increased nitrogen content in the soil, which is caused by the bacteria! Legumes are often planted by farmers to be a ‘cover crop’, due to the transformative power legume roots have on soil health.

2. Stem

Upwards and onwards we go! The stem is so much more than a green stalk. In some plants, they act as storage organs (e.g. potatoes) and in others they are crucial in the role of photosynthesis (e.g. cacti). However, there are some common characteristics that help the plant maximize rates of photosynthesis to ensure the biomolecules needed for respiration and reproduction are able to be synthesized.

The stem consists of three main regions: the node, internode, and the axillary bud. If you have ever seen the point at which leaves or branches attach to the main stem, that is the node, while internodes are the segments between nodes. The axillary bud is an embryonic shoot that grows in some plants.

The stem is home to what we call vascular tissues. These help transport amino acids, sugars, water and mineral ions around the plant to the different cells that may need them. The two types of vascular tissues that are most commonly seen are the xylem and phloem—we call this pair a part of the plant’s vascular system. The xylem transports water and dissolved minerals from roots to other parts of the plant, while phloem distributes the products of photosynthesis, such as glucose, from the leaves to the rest of the plant to be used for respiration. They are a bit like plumbing pipes housed within the stem - directing all the molecules to where they need to go!

3. Leaves

Leaves are probably the most well known plant organ there is, often being used as a representative symbol of plant life as a whole. These iconic structures are composed of several layers: the epidermis (outer layer), mesophyll (middle layer), and veins. Stacked like the tiers of a wedding cake, one on top of the other, each layer has adapted to aid the plant in photosynthesis. Within the epidermis, there is the waxy cuticle and upper and lower epidermis cells. Composed of lipids and hydrocarbon chains, the waxy cuticle helps the plant reduce water loss. Interestingly, it also acts as a physical barrier to prevent any pesky pathogens from entering. The waxy cuticle is generated by the epidermis cells, which have many chloroplasts that contain the chlorophyll pigment needed for photosynthesis! The mesophyll layer contains both palisade cells, which have high concentrations of chloroplasts as well as spongy mesophyll cells. While the palisade cells are organized compactly (often in regular rows and columns) to maximize the rate of photosynthesis, the spongy mesophyll cells have pockets of gas between them to allow for efficient gas exchange. That way, the plant is able to remove excess oxygen as a waste product and carbon dioxide can diffuse into the leaf cells to be used as a reactant in photosynthesis.

Additional Insights: Some plants have these needle-like outgrowths on their leaves called trichomes. These can offer protection against herbivores and environmental stress. Imagine being a herbivore… you wouldn’t want to bite down on a needle now, would you?

4. Flowers

Flowers are not only there as a great decoration for your home or garden. (Although, yes, who doesn’t love a good spread of flowers around them?!) For plants, they are so much more than areas that sit still and look pretty. Flowers are the reproductive organs of angiosperms (flowering plants) and consist of four main parts: sepals, petals, stamens, and pistils. Sepals are there to protect the flower bud from environmental damage or being eaten. In a lot of traditional diagrams you may have seen, it is the hard green casing present at the base of the flower. Whether rightly colored, impressively textured or astoundingly large, all petals are grown with one main purpose in mind: to attract pollinators. Pollinators are crucial for flowering plants, as they carry pollen from the stamen (male reproductive parts) of plants and transfer them to the pistils (female reproductive parts) which include the ovary, style, and stigma where pollen fertilization occurs. Both the stamen and pistils are also located within the flower, making it the key site where gametes fuse.

Extra Info: I am sure you are thinking “why do not all plants have flowers then?”. Well, there are different mechanisms for flowers to be pollinated. These include by wind or by insect pollination. For example, cereal crops are pollinated by the wind and so their pollen is much lighter than plants that are insect pollinated. That way, the likelihood of pollen being transported to another plant is much higher.

5. Fruit

Yum, yum it’s fruit time! Fruits develop from the ovary after fertilization and serve to protect and disseminate seeds. The fruit wall, or pericarp, can be divided into three layers: the exocarp (outer layer), mesocarp (middle layer), and endocarp (inner layer). Fruits can be classified as fleshy (e.g., apples) or dry (e.g., nuts).

Fruit for thought: Some fruits, such as burrs, have hooks that allow them to attach to animals that brush up against the plant. These animals transport these fruits to new environments, reducing the risk of competition between the parent plant and seed or fruit. These hooks were the inspiration for Velcro!

6. Seeds

Other than being a tasty snack or magical entitites that can grow into massive bean stalks, seeds are basically very very young plants. Theyconsist of an embryo, cotyledons (seed leaves), and a seed coat. The embryo is the section that develops into the plants that we see around us. The cotyledon and seed coat are there to help that embryo out. Cotyledons provide nutrients to the embryo during germination and the seed coat protects the embryo and helps prevent desiccation (drying out). Pretty cool, am I right?!

January 2023