Tissue is a term that refers to a group of cells that have a similar structure and function in an animal or plant. There are different types of tissues in animals and plants, such as muscle, nervous, epithelial, connective, vascular, ground, and epidermal tissues. Tissues are the building blocks of organs and other body parts. For example, your brain is made of nervous tissue, your heart is made of cardiac muscle tissue, and your skin is made of epithelial tissue.
Plant and animal tissues are different in many ways. Some of the main differences are:
- Plant tissues have a cell wall made of cellulose, which gives them rigidity and strength. Animal tissues do not have a cell wall, but a cell membrane made of proteins and lipids, which allows them to change shape and move.
- Plant tissues have chloroplasts, which are organelles that contain chlorophyll and perform photosynthesis. Animal tissues do not have chloroplasts, but mitochondria, which are organelles that produce energy by cellular respiration.
- Plant tissues are mainly divided into two types: meristematic and permanent. Meristematic tissues are composed of immature cells that can divide and differentiate into various types of tissues. Permanent tissues are composed of mature cells that have a specific function and structure. Animal tissues are mainly divided into four types: epithelial, muscle, connective, and nervous. Epithelial tissues cover the surfaces of organs and body cavities. Muscle tissues contract and relax to produce movement. Connective tissues bind and support other tissues and organs. Nervous tissues transmit and process electrical signals.
- Plant tissues have less energy and maintenance requirements than animal tissues, as plants do not move or perform complex activities. Animal tissues have more energy and maintenance requirements than plant tissues, as animals need to move, sense, and respond to their environment.
Plant tissues transport water and nutrients
Plant tissues transport water and nutrients by using specialized cells called xylem and phloem. Xylem is a tissue that transports water and minerals from the roots to the leaves. Phloem is a tissue that transports organic substances, such as sugars, from the leaves to the rest of the plant.
Xylem consists of long, hollow tubes that are connected end to end. Water moves through these tubes by a combination of osmosis, capillary action, and transpiration pull. Osmosis is the movement of water from a region of higher water potential to a region of lower water potential across a semi-permeable membrane. Capillary action is the movement of water along narrow spaces due to the attraction between water molecules and the walls of the spaces. Transpiration pull is the force generated by the evaporation of water from the stomata (tiny pores) of the leaves, which creates a negative pressure in the xylem.
Phloem consists of living cells that are connected by cytoplasmic strands called plasmodesmata. Organic substances move through these cells by a process called pressure flow. Pressure flow is driven by the difference in osmotic pressure between the source (where organic substances are produced or stored) and the sink (where organic substances are used or stored) of the phloem. The source cells load organic substances into the phloem, which lowers the water potential and causes water to enter by osmosis. This creates a positive pressure that pushes the organic substances along the phloem. The sink cells unload organic substances from the phloem, which raises the water potential and causes water to exit by osmosis. This reduces the pressure and allows more organic substances to enter from the source.