Unit 2 Multicellular Organisms

Unit Introduction

Welcome to the Multicellular Organisms unit, or as we like to call it....How do we work? Now that you know all about the internal workings of the cell, you're now going to explore the world of multicellular organisms - like you!

Billions of years ago, the first organisms began to appear which consisted of more than one cell. This confers certain advantages to the organism, such as the specialisation of different cells to different functions, but it also brings some problems. A single-cell organism is able to acquire all of the resources it needs directly from the environment through its membrane...but how on earth does a cell in the middle of your body get the oxygen and glucose it needs? And how can it get rid of the accumulating waste which would just diffuse out of a unicellular organism? We'll explore the systems which have arisen to deal with these sorts of issues in this unit.

Learning Outcomes

    • Specialisation of cells, in animals and plants, leads to the formation of a variety of tissues and organs.

    • Stem cells are the sites of production of specialised cells in animals and have the potential to become different types of cell.

      • Stem cells are involved in growth and repair.

    • Meristems are the sites of production of non-specialised cells in plants and are the only sites for cell division in a plant.

      • These cells have the potential to become any type of plant cell and they contribute to plant growth.

    • Nervous control

      • Nervous control in animals, including structure and function of central nervous system (CNS).

      • Brain structure: cerebrum, cerebellum and medulla.

      • Rapid reflex action and reflex arc: sensory, relay and motor neurons.

        • Receptors detect sensory input/stimuli.

        • Electrical impulses move along neurons.

        • A synapse occurs between neurons, allowing chemicals to transfer from one neuron to another.

    • Hormonal control

      • Endocrine glands release hormones into the blood stream.

      • Hormones are chemical messengers.

      • Target tissues have cells with receptors for hormones, so only some tissues are affected by specific hormones.

      • Blood glucose regulation to include insulin, glucagon, glycogen, pancreas and liver.

    • Body cells are diploid.

    • The structures and sites of gamete production in plants and animals.

    • The fertilisation of haploid gametes to produce a diploid zygote.

    • Comparison of discrete and continuous variation.

    • Most features of an individual phenotype are polygenic and show continuous variation.

    • Identification of phenotype and genotype, dominant and recessive characteristics and homozygous and heterozygous individuals.

    • Water is required for transporting materials and for photosynthesis.

    • Structures and processes involved in water movement to include root hairs, guard cells, stomata, epidermis, mesophyll cells and transpiration.

      • Water and minerals are transported up through the stem in xylem.

      • Xylem cells are lignified.

    • Sugar is transported up and down the plant in living phloem cells.

      • In mammals, nutrients, oxygen and carbon dioxide are transported in the blood.

    • Circulatory System

      • Pathway of blood through heart, lungs and body.

        • Heart structure to include right and left atria and ventricles.

        • Blood vessels to include: aorta, vena cava, pulmonary arteries and veins, and coronary arteries.

      • Arteries have thick, muscular walls, a narrow central channel and carry blood under high pressure.

      • Veins carry blood under low pressure; have thinner walls and a wide channel.

      • Veins contain valves to prevent backflow of blood.

      • Capillaries form networks at organs and tissues, and are thin walled and have a large surface area, allowing exchange of materials.

      • Red blood cells contain haemoglobin and are specialised to carry oxygen.

    • Respiratory System

      • Rings of cartilage keep airways open.

      • Oxygen and carbon dioxide are exchanged in the alveoli.

      • Alveoli have a large surface area, a good blood supply and thin walls to allow diffusion of gases.

      • Mucus traps dirt and microorganisms and cilia moves this up and out of the lungs.

    • Digestive System

      • Food is moved through the digestive system by peristalsis.

      • Villi in the small intestine are thin walled, have a large surface area and a good blood supply to aid absorption of glucose and amino acids.

      • The lacteals transport the products of fat digestion.

    • Effects of lifestyle choices on animal transport and exchange systems.

Source: SQA