Lesson Notes By Weeks and Term v5 - Grade 8
Systems for transporting substances in plants and animals – Week 5 focus
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Systems for transporting substances in plants and animals – Week 5 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Natural Sciences
Class: Grade 8
Term: 3rd Term
Week: 5
Theme: General lesson support
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Imagine a hot summer day in Gauteng. You grab an ice-cold Coke. That Coke needs to get from the shop to your hand, then into your mouth, and finally, the sugar and water inside need to get to all the cells in your body to give you energy and hydration. Similarly, a maize plant in the Free State needs to transport water from its roots to its leaves for photosynthesis. Both you and the maize plant rely on transport systems to survive. This week, we'll explore how plants and animals move vital substances around their bodies. Understanding these systems is crucial for understanding how organisms function, grow, and respond to their environment.
2.1 Transport in Plants: Plants need to transport water, mineral salts, and sugars throughout their bodies.
They have two main transport systems: Xylem: Xylem is responsible for transporting water and mineral salts from the roots to the leaves. This process is driven by transpiration, which is the evaporation of water from the leaves. This evaporation creates a "pull" that draws water up the xylem vessels. Imagine sucking liquid through a straw; transpiration is similar. Xylem cells are dead and hollow, forming continuous tubes. They have thickened cell walls containing lignin, which provides strength and support. Water and minerals travel upwards only through the xylem. The process of water moving upwards from the roots is also aided by capillary action, where water moves upwards within narrow spaces due to adhesion and cohesion forces. Root pressure, generated by the active absorption of mineral ions into the root cells, also contributes to pushing water upwards, though it's a less significant force than transpiration.
Phloem: Phloem is responsible for transporting sugars (produced during photosynthesis) from the leaves to other parts of the plant, such as the roots, stems, fruits, and flowers. This process is called translocation. Phloem cells are living, but they have specialized structures called sieve tubes and companion cells. Sieve tubes are long, cylindrical cells with perforated end walls called sieve plates. Companion cells are connected to sieve tubes and provide them with energy and support. Translocation occurs due to a pressure gradient, where sugars are actively loaded into the phloem in the leaves, increasing the sugar concentration and drawing water in by osmosis. This creates a high pressure in the source (leaves), which pushes the sugary sap to the sink (e.g., roots), where sugars are unloaded, reducing the pressure. The movement of substances in the phloem is bi-directional, meaning that substances can move both upwards and downwards depending on the plant's needs.
Example: Imagine a farmer in KwaZulu-Natal growing sugarcane. The sugarcane leaves produce sugar through photosynthesis. This sugar needs to be transported to the stem, where it is stored as sucrose. The phloem is the transport system that carries this sugar from the leaves to the stem. If the phloem is damaged (e.g., by insects), the sugar cannot be transported effectively, and the sugarcane yield will be reduced. 2.2 Transport in Animals (Humans): Humans have a complex circulatory system that transports blood, oxygen, nutrients, hormones, and waste products throughout the body. The circulatory system consists of the following components: Heart: The heart is a muscular organ that pumps blood around the body.
It has four chambers: two atria (upper chambers) and two ventricles (lower chambers). The atria receive blood from the veins, and the ventricles pump blood into the arteries. The heart contracts rhythmically, pushing blood through the circulatory system. The heart is responsible for maintaining blood pressure.
Blood Vessels: There are three main types of blood vessels: Arteries: Arteries carry blood away from the heart. They have thick, elastic walls that can withstand the high pressure of the blood being pumped from the heart. The largest artery is the aorta.
Veins: Veins carry blood back to the heart. They have thinner walls than arteries and contain valves that prevent blood from flowing backwards. The largest veins are the vena cavae.
Capillaries: Capillaries are tiny, thin-walled vessels that connect arteries and veins. They are the site of exchange of gases, nutrients, and waste products between the blood and the body's cells.
Blood: Blood is a fluid tissue that consists of plasma, red blood cells, white blood cells, and platelets.
Plasma: Plasma is the liquid component of blood and carries dissolved nutrients, hormones, and waste products.
Red Blood Cells (Erythrocytes): Red blood cells contain haemoglobin, a protein that binds to oxygen and transports it from the lungs to the body's cells.
White Blood Cells (Leukocytes): White blood cells are part of the immune system and help to fight infection.
Platelets (Thrombocytes): Platelets are involved in blood clotting. 2.3 Blood Circulation: Blood circulates through the body in two main circuits: Pulmonary Circuit: The pulmonary circuit carries blood between the heart and the lungs. Deoxygenated blood is pumped from the right ventricle of the heart to the lungs, where it picks up oxygen and releases carbon dioxide. Oxygenated blood then returns to the left atrium of the heart.
Systemic Circuit: The systemic circuit carries blood between the heart and the rest of the body. Oxygenated blood is pumped from the left ventricle of the heart to the body's cells, where it delivers oxygen and nutrients and picks up carbon dioxide and waste products. Deoxygenated blood then returns to the right atrium of the heart.