4 Transport in living things

• Many cells of multicellular organisms do not have direct contact with the surrounding environment, so they may not be able to obtain useful substances or remove waste substances fast enough through diffusion.
• Multicellular organisms require an efficient transport system to distribute useful substances such as oxygen, and dissolved nutrients to millions of cells in the body quickly.
• Transport in humans is called circulatory system.
• Three main components of circulatory system

  • heart
  • blood vessels
  • blood
• Blood flows in one complete circulation in the body, it passes through the heart twice called double circulation.
• Pulmonary circulation


  blood flowing between the heart and the lungs
• Systematic circulation


  blood flowing in the heart and the rest of the body
• The heart

  • funnel shaped, hollow, muscular organ
  • responsible to pump up blood to all parts of the body
  • valves present in the heart
  • blood flows in one direction
• Three types of blood vessels

  • arteries
  • veins
  • blood capillaries
• Arteries and veins are responsible for transport blood. No exchange of substances.
• Valves present in the veins ensure blood flowing in one direction and allow blood the return to the heart from the rest of the body.
• Capillaries

  • very thin and fragile
  • one-cell thick
  • act as the site of exchange of substances such as oxygen, carbon dioxide, nutrients and waste substances between blood and the body cells
• Pulmonary artery

  • from right ventricle to the lungs
  • deoxygenated blood
• Pulmonary vein

  • from lungs to left atrium
  • oxygenated blood
• Arteries

  • from left ventricle to rest of the body
  • oxygenated blood
• Veins

  • from rest of the body to right atrium
  • deoxygenated blood
• Why do arteries have thicker wall than veins?

  Blood flowing in the arteries is at a higher pressure because it needs to flow to the rest of the bodies. Hence a thicker wall is needed to withstand the high pressure of the blood.
• Why is the muscular wall in the left ventricle thicker than that of in the right ventricle?

  • The left ventricle needs to pump up blood the rest of the body, so it must exert a higher pressure to ensure blood can flow to greater distance.
  • The right ventricle pumps blood to the lungs which is a short distance, so it only needs to pump up blood at a low pressure.
• Why do veins have valves?

  The pressure of blood in the vein is very low, so the valves help the blood to move upwards against the gravity to reach the heart from the lower part of the bodies.
• Red Blood Cells


  • responsible for carrying oxygen from the lungs to various parts of the body
  • contain haemoglobin to help them transport oxygen more efficiently
  • carries small amount of carbon dioxide for removal
• Platelets


  • prevent blood loss from damaged blood vessels by forming clots
• White Blood Cells


  • part of the human immune system
  • help fight against diseases by destroying bacteria
• Blood Plasma


  • liquid part of the body
  • contains 90% water
  • transport substances in blood such as hormones, heat, dissolved nutrients, waste substances and carbon dioxide
• Xylem, phloem, and cambium are grouped together in vascular bundles in stems.
• Cambium produces new xylem and phloem tissues.
• Xylem tissues


  • made up of dead cells and have thick cellulose cell wall with lignin
  • a hollow vessel for water to flow in it
  • transport water and mineral salts from the roots to the stems and leaves
  • provide strength and support to the plant
• Phloem tissues


  • consist of living cells
  • involve in transporting food only
• Absorption of water

  • Roots are one of the organs responsible for absorbing water and dissolved mineral salts
  • many elongated structures are called root hairs
  • they increase the surface area
  • water and minerals can be absorbed into the plant at a fast speed
  • water enters the root hair cells by osmosis
• Transpiration is the evaporation of water from the leaves. It creates a transpiration pull to move water upwards along the xylem vessel from the roots to the leaves.
• During the depletion of dissolved mineral salts in soil, the root hair cell will use active transport.
• The phloem tissues will transport the food made in the leaves to all parts of the plant