I suppose that for most of you, your food comes from the supermarket since that’s where we generally buy our groceries. Other than that your food may come from a restaurant, cafeteria, roadside vendor, a factory or a farm. But that’s not what I mean when I ask where you food comes from. Food of course comes firstly from plants, the primary producers. Plants are known as autotrophs since they are able to harvest the energy from sunlight through photosynthesis to make their own food. They are able to do this because they have certain organelles called chloroplasts which contains a green light-trapping pigment called chlorophyll. If you remember, photosynthesis also requires carbon dioxide and water. At the end of the process, glucose is made which can be converted to other essential molecules.
The plants we eat are generally fruits and vegetables. The fruit is the seed-bearing part of the plant while vegetable refers to other parts such as the leaves (e.g. spinach), stem (e.g. celery), flower (e.g. cauliflower) and root (e.g. carrot). The fruit of the plant is formed when male reproductive cells in the flower fertilizes female reproductive cells located in the ovary. The male part of the plant is the stamen which consists of the filament and anther on which you will find pollen. The female part of the flower is the carpel which consists of the stigma style and ovary. Inside the ovary are the ovules which contains female reproductive cells. For fertilization to happen, male reproductive cells in the pollen must reach the ovary. This is facilitated by wind and pollinators such as bees, wasps and other insects that brush against the anther, capturing pollen on their surface and then landing on the stigma where the pollen gets stuck. From here, the pollen can start its journey to the ovary. The pollen has two cells, the generative cell and the tube cell. The tube cell is responsible for drilling a tube down to the ovary while creating a path for the generative cell. During its travel, the generative cell divides into two. When they reach the ovary, one of the cells fuses with the female egg in the ovary to form a zygote. This is known as fertilization. The second male cell fuses with two other calls in the ovary which are together known as the polar nuclei. This fusion results in the development of the embryo. This is the part of the fruit that grows around the seed which humans and animals may eat. By eating the fruit and discarding the usually inedible seeds, animals help to disperse them. In this way, the plant is able to survive to pass on its genes.
Many plants are able to self-pollinate. That happens when pollen from a flower fertilizes the ovary on the same flower. However, this does not make for strong and resistant genes. If the plant keeps passing on the same genes they will have the same set of disadvantages. For example if it is not resistant to a certain fungal infection, then they can all be wiped out at once if this problem comes into play. Hence, to ensure genetic variation, plants prefer to be cross-pollinated. This happens when pollinators take pollen from one plant to another plant. Some plants may encourage this by having only a male or female flower. One example is the kiwi plant. The female plant cannot bear fruit unless it gets pollen from a non-fruit-bearing male plant. Some plants that have both male and female flowers have developed unique mechanisms to prevent cross-pollination. For example avocado flowers have both male and female parts, but both are not accessible at the same time. For example, when the female part is exposed during the day, the male part is closed, and vise versa. In this way, fertilization will most likely occur across trees rather than on the same tree.
As primary producers, plants are the first step in the food chain. They are followed by primary and secondary consumers. Primary consumers are animals that eat plants. Secondary consumers are the animals that eat the animals that eat the plant. For example, the chicken eat the insect that eat the plant. Primary consumers that are a staple in the diet include, cattle, goat and sheep. Secondary consumers generally consumed eaten include poultry and fish.