variation

Variation in Species

Overview of Variation

• Variation refers to the differences within and between species. It describes how different individuals exhibit diverse characteristics, influenced by either inherited traits, environmental factors, or a combination of both.

Continuous vs. Discontinuous Variation

• Continuous Variation: This type of variation allows characteristics to take any value within a range. Examples include height, weight, body mass, hair length, and arm span. These traits can be plotted on a histogram and typically show a normal distribution curve.

• Discontinuous Variation: This variation occurs when characteristics can only take on specific, defined values with no intermediate possibilities. Examples include sex (male or female), blood group, and eye colour. Such traits are best represented on a bar chart, as they do not exhibit a normal distribution curve.

Representation of Variation

Graphical Representation of Variations

• Bar Chart: Used for discontinuous data. Features spaces between bars to indicate distinct categories without a normal curve distribution.

• Histogram: Used for continuous data. Bars touch each other without spaces, representing a continuous range of values with potential for a normal distribution curve.

Example Cases

• Robert Wadlow: A notable example of continuous variation; he was the tallest recorded person at 2.72 meters, illustrating significant differences in human height.

Types of Variation: Inherited and Environmental

Definitions

• Inherited Variation: Differences in organisms arising from genetic factors passed down from parents. Examples include eye colour, lobed ears, and sporting ability.

• Environmental Variation: Differences resulting from environmental influences such as diet, education, or injury. Examples include weight, hair colour (dyed), and certain health conditions like diabetes.

Variation Examples

• Inherited Traits: Eye colour, lobed ears.

• Environmental Traits: Weight, religion, accent.

• Both: Intelligence, sporting ability, skin colour.

• Several characteristics may stem from both inherited and environmental influences.

Investigating Variation in the Classroom

Class Practical: Arm Span Investigation

1. Prediction: Determine whether arm span shows continuous or discontinuous variation.

2. Equipment Needed: Measuring tape, notebooks for recording data.

3. Method Followed: Measure the arm span of each student and record the results systematically.

4. Variables in the Investigation: Independent variable (student identity), dependent variable (arm span measurement).

5. Data Recording: Use a tally system to systematically document measurements.

Analysis of Class Data

1. Type of Variation: Classify arm span as continuous or discontinuous.

2. Range of Arm Span: Identify the largest and smallest measurements from the class.

3. Class Patterns: Describe trends or common measurements observed among students.

4. Contributing Factors: Discuss the influence of inherited genes versus environmental conditions on observed arm spans.

Quick Check Questions and Challenges

Review Questions

1. Define discontinuous variation and give an example.

2. Define continuous variation and give an example.

3. Identify the correct graphical representation for discontinuous data (Bar Chart).

4. Identify the correct graphical representation for continuous data (Histogram).

Classification Tasks

• Classify characteristics (e.g., length of arm, hair colour, shoe size), determining whether they fall under continuous or discontinuous variation.

Challenge

• Elaborate on the distinction between continuous and discontinuous variation, providing detailed analysis and examples for better understanding.

Microscope Slides for Viewing Plant Cells: Preparing Onion Slides 1. Cut/Peel the Onion: Using a forceps or scalpel, gently peel back the onion to reveal the inner parts. Scale the onion to be very thin for the light to pass through. 2. Add a Drop of Juice: On a clean microscope slide, add a drop of onion juice, ensuring visibility and contrast. 3. Cover with a Cover Slip: Place the cover slip onto the drop at an angle to avoid bubbles. 4. Examine Under Microscope: Carefully place the slide onto the stage and enjoy viewing the onion cells under the microscope. ### Microscope Slides for Viewing Animal Cells: Preparing Cheek Cell Slides 1. Take a Cotton Swab: Gently rub it on the inside of your cheek. 2. Transfer to Slide: Roll the cotton swab onto the microscope slide to transfer cheek cells. 3. Add a Drop of Stain: To highlight the cells, add a drop of methyl blue solution. 4. Cover with a Cover Slip: Place the cover slip carefully over the specimen. 5. View Under Microscope: Place the slide onto the stage and enjoy viewing the cheek cells under the microscope.

Specialised Cells

Sperm Cell

• Function: to fertilise an egg cell

• Found in: the testes

• A sperm is streamlined and has a long tail that provides thrust so it can swim and find an egg cell.

• The nucleus contains half a set of genes.

Egg Cell

• Function: to be fertilised by sperm

• Found in: the ovaries

• Contains yolk, which provides a large amount of food for the new cell being formed.

• The nucleus contains half a set of genes.

Muscle Cell

• Function: to move organs

• Found in: muscles

• Gets energy by respiration.

Ciliated Cell

• Function: to clean your lungs

• They line the air passages in the lungs.

• They have tiny hairs called cilia.

• Hairs sweep mucus with trapped dust and bacteria back up the throat.

Root Hair Cell

• Function: to store water and minerals

• Has a large surface which helps it to absorb water and minerals.

• Thin cell wall makes it easy for water to pass through.

Nerve Cell

• Function: send impulses to the brain

Cell division is a process where cells increase in size, then divide into two new cells. It is vital for growth and repair, because cells must have been damaged or because there aren't enough cells.