bio

Comparing Your Body to a City

Just like a city needs various systems and workers to function—such as energy supply, waste disposal, law enforcement, and city hall—your body also needs systems to maintain life. These tasks are carried out by specialized cells, much like how different city jobs are handled by trained professionals.

🧬 Specialized Cells

• Definition: Specialized cells have specific physical and chemical traits that enable them to perform unique functions in the body.

• Origin: Specialized cells develop from stem cells, which are found in:

  • Embryos

  • Umbilical cords

  • Some adult tissues (e.g., bone marrow)

• Cell Stats:

  • Your body contains 50–75 trillion cells

  • There are about 220 different types of specialized cells

🧪 Examples of Specialized Cells

1. Nerve Cells

   • Function: Conduct electrical impulses

   • Role: Coordinate activities throughout the body

2. Skin Cells

   • Function: Protect internal cells and reduce water loss

   • Note: Can be damaged by injuries like burns

3. Muscle Cells

   • Function: Enable movement

   • Roles: Locomotion, speech, digestion, blood circulation, facial expressions

4. Sperm and Egg Cells

   • Function: Reproduction

   • Note: Sperm cells can move independently

Cell Division and the Cell Cycle

🎯 Learning Goals

By the end of the lesson, students should be able to:

• List 3 reasons for cell division

• Understand the difference between sexual and asexual reproduction

• Describe the cell cycle, including the stages of mitosis

• Draw or identify the stages of mitosis

🧪 3 Reasons for Cell Division

Use the acronym GRR:

1. Growth

   • As cells grow, diffusion becomes too slow.

   • Smaller cells are more efficient at moving nutrients and waste.

   • Division increases surface area and efficiency.

2. Repair & Replacement

   • Damaged or dead cells are replaced through cell division.

3. Reproduction

   • Asexual Reproduction

     • One parent

     • Offspring are genetic clones

     • Occurs in bacteria, houseleek, aspen, etc.

   • Sexual Reproduction

     • Two parents, involves gametes (egg and sperm)

     • Offspring are genetically unique

     • Occurs in complex organisms (horses, flowers, etc.)

🧬 Key Terminology

🔄 The Cell Cycle

Divided into three major stages:

Stage I: Interphase

• Longest phase

• Cell is not dividing

• Normal activities (growth, respiration)

• DNA and organelles replicate near the end

⚙ Stage II: Mitosis

(Mitosis = division of the nucleus, not the entire cell)

IIa: Prophase

• DNA condenses into chromosomes (sister chromatids)

• Nuclear membrane breaks down

IIb: Metaphase

• Chromosomes line up along the middle (equator) of the cell

IIc: Anaphase

• Sister chromatids separate and move to opposite poles

• Now called daughter chromosomes

IId: Telophase

• Daughter chromosomes unwind back into chromatin

• Nuclear membrane reforms

• Two new nuclei begin to form

✂ Stage III: Cytokinesis

(Division of the cytoplasm)

• Starts during late Telophase

• Plant cells: A cell plate forms (becomes new cell wall)

• Animal cells: Cell membrane pinches in to form two cells

⚠ Note:

• Interphase and Cytokinesis are not part of mitosis but are part of the overall cell cycle.

The Nervous System

🔹 Main Parts of the Nervous System

1. Central Nervous System (CNS)

   • Includes the brain and spinal cord

   • Protected by the skull and spine

2. Peripheral Nervous System (PNS)

   • Includes all nerves outside the CNS

   • Carries signals to:

     • Voluntary muscles

     • Sensory organs

     • Involuntary functions (like heartbeat or digestion)

⚡ Nerve Tissue & Neurons

• Made up of specialized cells called neurons

• We have approximately 100 billion neurons

• Function: Conduct electrical signals from one part of the body to another

🧪 Key Features:

• Neurons: Conduct signals in only one direction

• Nerves: Can carry signals in both directions

• Myelin Sheath: Fatty material that insulates electrical impulses

• Nerve Repair: Nerves do not regenerate as easily as other body tissues

🧲 Sensory Receptors

• Detect pressure, temperature, and pain

• Send information to the brain, which processes signals in specialized regions

🦾 The Bionic Arm

• A modern prosthetic that responds to thought

• Works by rerouting nerve signals from the brain to the prosthetic limb

🚨 Disorders of the Nervous System

1. Multiple Sclerosis (MS)

   • Destroys the myelin sheath

   • Symptoms:

     • Muscle weakness

     • Slurred speech

     • Difficulty walking

2. Paralysis

   • Caused by damage to the nervous system

   • Results in loss of muscle function and/or sensation

The Digestive System

🔄 Main Functions

• Takes in food

• Digests it (mechanically & chemically)

• Absorbs nutrients

• Excretes waste

🧠 Structure

• Made up of:

  • The digestive tract

  • Accessory organs (like the liver and pancreas)

🦷 1. The Mouth

• Mechanical digestion: Teeth and tongue break down food

• Chemical digestion: Enzymes in saliva start breaking down carbohydrates

🧪 2. The Esophagus

• A muscular tube connecting the mouth to the stomach

• Moves food using peristalsis (wave-like contractions of smooth muscle)

🥣 3. The Stomach

• Churns food using smooth muscle tissue

• Digestive enzymes and acid are secreted by stomach lining cells

• Nerves around the stomach send signals when you're full (satiated)

🧬 4. The Small Intestine

• Around 6 meters long

• Main site of nutrient absorption

• Nutrients enter the bloodstream through the walls

• Moves food along using peristalsis

💩 5. The Large Intestine (Colon), Rectum, and Anus

• About 1.5 meters long

• Absorbs water from undigested food

• Remaining material becomes feces, stored in the rectum

• Feces exit the body through the anus

🧫 Accessory Organs

The Circulatory System (Cardiovascular System)

🔄 Main Functions

• Transports nutrients, oxygen (O₂), carbon dioxide (CO₂), and waste

• Regulates body temperature

• Delivers white blood cells to fight infection

🩸 3 Main Parts of the Circulatory System

1. Blood

A connective tissue made up of four components:

2. The Heart

• Made of cardiac muscle, nerves, and connective tissue

• Has 4 chambers and 4 valves

• Pumps blood out through arteries and receives blood through veins

• The heartbeat ("lubb-dubb") is caused by valve movement

Heart Rate is the number of beats per minute, influenced by:

• Physical activity

• Age

• Stress

• Temperature

• Overall health

Measuring Heart Rate: Count beats for 10 seconds and multiply by 6.

3. Blood Vessels

🩺 Blood Pressure

• Measured with a sphygmomanometer (BP cuff)

• Expressed as systolic / diastolic (e.g., 120/80 mmHg)

🧪 Diagnostic Tests

The Respiratory System

🔄 Main Functions

• Brings in oxygen (O₂) for cellular respiration

• Removes carbon dioxide (CO₂) — a waste product of respiration

• Moves over 10,000 L of air through the lungs each day

😮‍💨 How Breathing Works

Inhalation (Breathing In)

• Rib muscles and diaphragm contract

• Chest cavity volume increases

• Air pressure drops → air flows into lungs

Exhalation (Breathing Out)

• Muscles relax

• Chest cavity volume decreases

• Air pressure rises → air is pushed out

🌟 Special Features of the Respiratory System

🫁 Gas Exchange

• Takes place in the alveoli (tiny air sacs in the lungs)

• Oxygen (O₂) diffuses from alveoli → capillaries

• Carbon dioxide (CO₂) diffuses from capillaries → alveoli

• Surrounded by a network of capillaries to maximize exchange

🐟 Respiratory System in Fish

• Gills are used instead of lungs

• The same diffusion process of oxygen and carbon dioxide applies

🚭 Impact of Smoking

• Although not detailed here, smoking damages cilia, increases mucus, and harms alveoli

• Leads to reduced lung function and increased risk of diseases like lung cancer and COPD

Describe the function of each organelle

 Centroil-

It plays a crucial part in cell division. It specifically organizes microtubules that serve as the cell's skeletal system. They help determine the location of the nucleus and other organelles in the cell. It's found in animal cells.

Cell wall-

The cell wall's function is to provide support, shape, and protection, it is the structural layer outside the membrane. The cell wall is found in both plant and animal cells

Choroplast-

Chloroplasts are the site of photosynthesis. They also play a role in synthesizing amino acids, fatty acids, and lipids. They are found in plant cells.

Mitochondria-

The mitochondria are the powerhouse of the cell, providing all of the energy for the cell. Both plant and animal cells.

Chromosomes-

They primarily function as carriers of genetic information in a cell; they house DNA, ensure the accurate transmission of this genetic material during cell division, and are crucial for cellular processes like replication and division. Both plant and animal cells.

Goldgi bodies-

They act as the processing and packaging centers for proteins and lipids, especially those destined for export from the cell. Modify, sort, and package these little molecules into vessels for transport to various destinations in the cell for secretion outside. Found in both plant and animal cells

Vacuole- 

Works as a storage unit and also plays a role in cell structure and homeostasis. Also found in both plant and animal cells.

Cell membrane-

Its function is to act as a protective barrier, regulate what enters and exits the cell, and facilitate communications with other cells. It allows essential nutrients and waste products to be transported, and blocks harmful substances from entering. It is found in both plant and animal cells.

Nuclear membrane-

The nuclear membrane is the same as the cell wall, controlling what comes in and out, but for the nucleus instead. This means that it is found in both plant and animal cells.

Nucleus-

The nucleus is the control center of the cell and also houses the DNA or genetic material. It regulates gene expression, controls cell division, and directs the synthesis of proteins.