2nd Term Week 2
Class: SS 1
Subject : Biology
Topic: Some Properties and Functions of the Cells
Learning Objectives : By the end of the lesson, learners will be able to :
i. Identify the properties of cells.
ii. Explain each of the properties listed above in details.
iii. State the functions of the cells in relation to their properties.
Content:
1. Nutrition (Feeding)
Nutrition is the process by which food is taken in by living organisms in order to supply the nutrients required for the continuous metabolic reactions going on in the body. Food is the source of nutrients.
Usefulness of food: Living cells or organisms require food for various reasons. These reasons are:
i. To provide energy needed for various physical and metabolic activities
ii. To make essential substances such as hormones and enzymes.
iii. To make new cells for growth and replacement of worn-out tissues.
Types of Nutrition: The two major types of nutrition are autotrophic and heterotrophic nutrition.
Autotrophic nutrition is a process in which the organism produces their food from the simple inorganic materials such as water, carbon dioxide and mineral salts in the presence of sunlight. They make their own food with the help of the water, solar energy, and carbon dioxide by the method of photosynthesis. Some examples of autotrophs are Algae, Phytoplankton, Seaweed, Wheat, Grass, Maize plant, bacteria, blue-green algae, and Cyanobacteria. All plants have a mode of autotrophic nutrition to keep producing their own food.
Heterotrophic nutrition is a mode of nutrition in which organisms depend upon other organisms for food to survive. They can’t make their own food like Green plants. Heterotrophic organisms have to take in all the organic substances they need to survive. Common examples of heterotrophs include animals, fungi and bacteria. There are four different types of heterotrophs which include herbivores, carnivores, omnivores and decomposers.
2. Cellular Respiration:
Cellular respiration involves the chemical activities of the cells in which glucose is broken down by a series of reactions controlled by enzymes to release energy. The energy so released is stored in adenosine trisphosphate (ATP). ATP is the form in which energy is carried, stored and used by all living cells for various metabolic processes.
Types of Cellular respiration:
There are two main types of cellular respiration. These are: aerobic and anaerobic respiration.
a.) Aerobic respiration: Aerobic respiration is the type of respiration which requires oxygen to break down glucose into water, carbon dioxide and energy (ATP). The breaking down of glucose in the body passes through several pathways before it can produce energy. These pathways are Glycolysis and Kreb’s cycle.
i. Glycolysis is a series of chemical reaction which involves the breaking down of glucose to a 3-caebon molecule called pyruvic acid. During glycolysis, no oxygen is required, and it takes place in the cytoplasm of the cells. Very little energy is produced. A net formation of 2 ATPs are produced from complete oxidation of one glucose molecule during glycolysis.
ii. Kreb’s cycle: The kreb’s cycle is also known as Citric Acid Cycle or Tricarboxylic Acid Cycle (TAC). This involves a series of cyclic reactions which begins with the pyruvic acid formed from glycolysis which combined with acetyl co-enzyme A to form citric acid. Kreb’s cycle alone produces a total net of 36 ATPs.
b.) Anaerobic respiration: This is the type if respiration which does not require the presence of oxygen to provide energy. During anaerobic respiration, glucose is broken down to yield carbon dioxide, alcohol (ethanol) and energy. The process by which glucose is broken down to alcohol in the absence of oxygen id called fermentation. Yeasts exhibit anaerobic respiration.
3. Excretion:
Excretion is defined as the process by which organisms get rid of waste products during its metabolism. The reason for excretion by all living things is to get rid of metabolic wastes which are poisonous or toxic to the body system when they are not removed. The table below shows the excretory organs/ organelles of some organisms.
Plants produce waste products in the form of two gases i.e. oxygen during photosynthesis and carbon dioxide during respiration. They excrete these gases through a structure called stomata. Animals have an excretory system consisting of a couple of kidneys, ureter, urinary bladder and urethra.
4. Growth: