Biology Notes - Cell Biology PDF

## Cell - The Unit of Life - **Discovery of the cell:** - **Robert Hooke (1665):** Discovered cells in cork slices. - **Leeuwenhoek (1674):** First to observe living cells in pond water. - **Robert Brown (1831):** Discovered the nucleus in plant cells. - **Purkinje (1839):** Coined...

## Cell - The Unit of Life - **Discovery of the cell:** - **Robert Hooke (1665):** Discovered cells in cork slices. - **Leeuwenhoek (1674):** First to observe living cells in pond water. - **Robert Brown (1831):** Discovered the nucleus in plant cells. - **Purkinje (1839):** Coined the term "protoplasm" for the fluid substance of the cell. - **Virchow (1855):** Proposed that all cells arise from pre-existing cells. - **Schleiden and Schwann (1838-39):** Formulated the cell theory, which states that: - all living organisms are composed of one or more cells. - the cell is the basic unit of structure and function in living organisms. - all cells arise from pre-existing cells. ### Types of Cells - **Unicellular:** - Composed of one cell. - Single cell performs all life functions. - Examples: Amoeba, Bacteria, Chlamydomonas, Paramesium. - **Multicellular:** - Composed of more than one cell. - Division of labor, with specialized cells performing specific functions. - Examples: Plant, Animal, Fungi. - **Division of Labor:** - Seen even within single-celled organisms. - **Largest cell:** Ostrich egg. - **Longest cell:** Neurons. - **Smallest cell:** Mycoplasma. ### Structure of a Typical Plant Cell - **Cell wall:** Outermost layer, providing structural support and protection. - **Plasma membrane:** Thin, selectively permeable membrane regulating entry and exit of substances into the cell. - **Cytoplasm:** Gel-like substance containing organelles, responsible for various cellular activities. - **Nucleus:** Control center containing DNA, responsible for inheritance and control of cellular functions. - **Nucleolus:** Dense structure within the nucleus, related to ribosome formation. - **Chromatin:** Thread-like structures composed of DNA and proteins, responsible for inheritance. - **Chromosomes:** Tightly packed, condensed chromatin visible during cell division. - **Nuclear membrane:** Double membrane separating the nucleus from the cytoplasm, with pores for exchange of material. - **Ribosomes:** Sites of protein synthesis. - **Endoplasmic Reticulum (ER):** - **Rough ER:** Contains ribosomes and helps in protein synthesis and transport. - **Smooth ER:** Involved in lipid synthesis, detoxification, and carbohydrate metabolism. - **Golgi apparatus:** Modifies, sorts, and packages cellular products for secretion. - **Mitochondria:** Powerhouse of the cell, responsible for ATP production. - **Chloroplast:** Site of photosynthesis in plants, containing chlorophyll for capturing light energy. - **Lysosome:** Contains digestive enzymes responsible for breaking down cellular waste and debris. - **Vacuole:** Fluid-filled sacs, primarily for storing water and other substances, and maintaining cell turgor pressure. ## Transport Across the Cell Membrane - **Diffusion:** Movement of substances from a region of higher concentration to lower concentration. - **Osmosis:** movement of water from a region of higher water concentration to lower water concentration across a semipermeable membrane. - **Absorption of Water:** Movement of water from the environment into plant roots. ## Cell Membrane - Importance - **Selectively permeable:** Allows only specific substances to pass through, regulating cellular activities. - **Flexible:** Enables cells to engulf food and other materials through **endocytosis**, a process of taking in substances. - **Protection:** Provides a barrier against the external environment. ### Types of Cells Based on Cell Membrane & Nucleus - **Prokaryotes:** - Lack a nuclear membrane, with their genetic material present in a nucleoid region. - Examples: Bacteria, Mycoplasma, blue-green algae, and Archaea. - **Eukaryotes:** - Possess a well-defined nucleus with a nuclear membrane, along with other membrane-bound organelles. - Examples: Plants, animals, fungi, protists. ### Organelles Common to Both Prokaryotes & Eukaryotes - **Ribosomes:** Site of protein synthesis. - **Cell wall (in some):** Provides structural support and protection. ## Cell Division - The process of cell division produces new cells for growth, repair, and reproduction. - Two main types of cell division: - **Mitosis:** Asexual division resulting in two identical daughter cells, containing the same number of chromosomes as the parent cell. - **Meiosis:** Occurs in specialized cells for sexual reproduction, resulting in four daughter cells, each with half the number of chromosomes as the parent cell. ### Stages of Mitosis - **Interphase:** The cell grows, replicates its DNA, and prepares for division. - **Prophase:** Chromosomes condense and become visible, nuclear membrane disappears. - **Prometaphase:** Spindle fibers attach to chromosomes, and the chromosomes start moving towards the center. - **Metaphase:** The chromosomes align at the center of the cell, forming the metaphase plate. - **Anaphase:** The sister chromatids of each chromosome separate and move towards opposite poles. - **Telophase:** The chromosomes reach the poles, nuclear membrane reforms, and the cytoplasm divides (cytokinesis) to form two daughter cells. ### Stages of Meiosis - **Meiosis I:** - *Prophase I:* Chromosomes condense, homologous chromosomes pair up, and crossing over occurs. - *Metaphase I:* Homologous chromosomes align at the center. - *Anaphase I:* Homologous chromosomes separate. - *Telophase I:* Two daughter cells are formed. - **Meiosis II:** - *Prophase II:* Chromosomes condense again. - *Metaphase II:* Chromosomes align at the center. - *Anaphase II:* Sister chromatids separate. - *Telophase II:* Four haploid daughter cells are formed. ### Importance of Mitosis and Meiosis - **Mitosis:** Essential for growth, repair, and asexual reproduction. - **Meiosis:** Essential for sexual reproduction and genetic diversity. ## Tissues - A group of similar cells working together to perform a specific function. ### Types of Tissues - **Plant Tissues:** - **Meristematic:** Composed of actively dividing cells responsible for growth of the plant. - **Apical meristem:** Found at the tips of roots and stems, responsible for increasing length. - **Lateral meristem:** Responsible for increasing girth. - **Intercalary meristem:** Found at the base of leaves, responsible for increasing length. - **Permanent:** Mature cells specialized for specific functions. - **Simple Tissues:** Composed of one type of cell. - **Parenchyma:** Thin-walled cells for storage, photosynthesis, and other functions. - **Collenchyma:** Thickened cells for support and flexibility, found in stems and leaves. - **Sclerenchyma:** Thick, lignified cells for strength and support, found in seed coats and vascular bundles. - **Complex Tissues:** Composed of more than one type of cell. - **Vascular Tissue:** Responsible for transport of water and nutrients. - **Xylem:** Conducts water upwards. - **Phloem:** Conducts food downwards. - **Animal Tissues:** - **Epithelial:** Found lining external and internal surfaces, providing protection, secretion, and absorption. - **Connective:** Supports and binds different tissues and organs. - **Blood:** Fluid connective tissue, transporting oxygen, nutrients, hormones, and waste products. - **Bone:** Strong supportive tissue. - **Cartilage:** More flexible than bone, providing support and cushioning. - **Areolar:** Loosely packed connective tissue, found beneath the skin. - **Adipose:** Stores fat. - **Muscular:** Responsible for movement. - **Skeletal:** Attached to bones, responsible for voluntary movements. - **Smooth:** Found in internal organs, responsible for involuntary movements. - **Cardiac:** Found only in the heart, responsible for involuntary blood circulation. - **Nervous:** Responsible for communication and coordination within the body. ## Nutrition in Human Beings - **Nutrition:** The process of taking in, breaking down, and absorbing nutrients from food. - **Digestion:** The process of breaking down food into smaller molecules that can be absorbed. - **Nutrients:** Substances that the body needs for growth and repair, and to provide energy. ### Digestive System - **Mouth:** - Mechanical breakdown of food through chewing. - Chemical breakdown of **starch** by **salivary amylase**. - **Oesophagus:** Muscular tube that carries food from the mouth to the stomach. - **Stomach:** - Mechanical churning of food. - Chemical breakdown of **proteins** by **pepsin** and **hydrochloric acid**. - **Small intestine:** - Major site of nutrient absorption. - **Duodenum:** First part, receives secretions from the pancreas and liver. - **Pancreatic juice:** Contains enzymes like **trypsin** (for protein digestion), **amylase** (for carbohydrate digestion), and **lipase** (for fat digestion). - **Bile:** Emulsifies fats, making them easier to digest. - **Jejunum:** Middle part. - **Ileum:** Last part, absorbs most of the remaining nutrients. - **Large intestine:** Absorbs water and forms faeces. - **Rectum:** Stores faeces before excretion. - **Anus:** Opening at the end of the digestive tract for the elimination of faeces. ## Respiration - The process of taking in oxygen and releasing carbon dioxide. - Occurs in all living organisms. - **Breathing:** The mechanical process of inhaling oxygen and exhaling carbon dioxide. - **Lungs:** Primary respiratory organs in humans. - **Diaphragm:** Muscular sheet separating the chest cavity from the abdominal cavity. - **Rib cage:** Protective structure that surrounds the lungs. - **Alveoli:** Tiny air sacs in the lungs where gas exchange occurs. - **Cellular respiration:** The process of breaking down glucose to produce energy (ATP) in the form of ATP. - **Aerobic respiration:** Requires oxygen. - **Anaerobic respiration:** Occurs without oxygen. ## Excretion - The process of removing waste products from the body. - Necessary for maintaining homeostasis. - **Excretory system:** Organs involved in excretion. - **Kidneys:** Main organs of excretion, filtering blood and producing urine. - **Ureters:** Carry urine from the kidneys to the bladder. - **Urinary bladder:** Stores urine before it is excreted.. - **Urethra:** Carries urine from the bladder to the outside. ## Coordination and Control - The process by which different parts of the body work together to maintain homeostasis. - Two main systems involved in coordination and control: - **Nervous system:** Fast-acting, using electrical impulses to transmit information. - **Endocrine system:** Slower-acting, using hormones to transmit information. ### Nervous System - **Central nervous system (CNS):** - **Brain:** Control center, responsible for processing information, making decisions, and initiating actions. - **Spinal cord:** Connects the brain to the rest of the body, also responsible for some reflex actions. - **Peripheral nervous system (PNS):** Network of nerves that carry information to and from the CNS. - **Cranial nerves:** Connect the brain to the head and neck. - **Spinal nerves:** Connect the spinal cord to the rest of the body. ### Neuron - **Neuron:** The basic unit of the nervous system, responsible for transmitting nerve impulses. - **Cell body (soma):** Contains the nucleus. - **Dendrites:** Receive impulses from other neurons. - **Axon:** Transmits impulses away from the cell body. ### Types of Neurons - **Sensory neurons:** Carry impulses from sensory organs to the CNS. - **Motor neurons:** Carry impulses from the CNS to effectors (muscles or glands). - **Interneurons:** Connect neurons within the CNS. ### Reflex Action - A rapid, involuntary response to a stimulus. - Bypasses the brain, involving only the spinal cord. - Essential for quick responses to protect the body from injury. ## Reproduction - The process by which living organisms produce new individuals of their own kind. - **Sexual reproduction:** Involves the combination of genetic material from two parents, resulting in offspring with greater genetic diversity. - The process involves the formation of gametes (sperm and egg) through meiosis. - Fertilization is the fusion of a sperm and an egg to form a zygote. - **Asexual reproduction:** Involves only one parent, resulting in offspring that are genetically identical to the parent. ### Methods of Reproduction - **Fission:** - **Binary fission:** The parent cell divides into two identical daughter cells. - **Multiple fission:** The parent cell divides into more than two daughter cells. - **Budding:** - A new individual develops as an outgrowth from the parent. - **Spore formation:** - Specialized reproductive cells that can develop into new individuals. - **Fragmentation:** - The body of the parent organism breaks into fragments, each capable of growing into a new individual. - **Vegetative propagation:** - In plants, new individuals arise asexually from vegetative parts like stems, roots, or leaves. ### Sexual Reproduction in Flowering Plants - **Flower:** The reproductive organ. - **Stamen:** Male reproductive organ. - **Anther:** Produces pollen grains containing male gametes. - **Pistil:** Female reproductive organ. - **Stigma:** Receives pollen grains. - **Style:** Connects the stigma to the ovary. - **Ovary:** Contains ovules. - **Pollination:** The transfer of pollen grains from the anther to the stigma. - **Cross-pollination:** Pollen is transferred from the anther of one flower to the stigma of another flower. - **Self-pollination:** Pollen is transferred from the anther of a flower to the stigma of the same flower. - **Fertilization:** The fusion of a male gamete (sperm) with the egg cell in the ovule, forming a zygote. - **Seed:** The fertilized ovule containing the zygote, surrounded by a protective seed coat. - **Fruit:** The mature ovary, often containing seeds. ### Sexual Reproduction in Humans - **Puberty:** The period of sexual maturation. - **Male:** Production of sperm cells. - **Female:** Production of egg cells. **Male Reproductive System** - **Testes:** Produce sperm cells. - **Scrotum:** A pouch-like structure that holds the testes. - **Epididymis:** A coiled tube where sperm cells mature and are stored. - **Vas deferens:** A tube that carries sperm from the epididymis to the urethra. - **Urethra:** A tube that carries both urine and sperm from the body. - **Prostate gland:** Secretions nourish and activate sperm. - **Seminal vesicle:** Secretions provide lubrication for sperm. **Female Reproductive System** - **Ovaries:** Produce egg cells. - **Oviducts (Fallopian tubes):** Carry eggs from the ovary to the uterus. - **Uterus:** A muscular organ where a fertilised egg implants and develops into a fetus. - **Cervix:** The opening to the uterus, which widens during childbirth. - **Vagina:** A muscular canal that connects the uterus to the outside and serves as the birth canal. ## Heredity and Evolution - **Heredity:** The transmission of traits from parents to offspring. - **Genetics:** The study of heredity and variation. - **Evolution:** The gradual change in the characteristics of a species over time. ### Genes & Chromosomes - **Genes:** Units of heredity, responsible for specific traits. - **Chromosomes:** Thread-like structures composed of DNA and proteins that carry genes. - **Alleles:** Different forms of a gene. ### Key Terms - **Genotype:** The genetic makeup of an organism. - **Phenotype:** The observable characteristics of an organism. - **Homozygous:** Having two identical alleles for a particular trait. - **Heterozygous:** Having two different alleles for a particular trait. - **Dominant allele:** An allele that masks the effect of the recessive allele. - **Recessive allele:** An allele that is masked by the dominant allele. ### Gregor Mendel & Pea Plant Experiment - Gregor Mendel, the "Father of Genetics," conducted experiments using pea plants to study inheritance. - He discovered the basic principles of inheritance: - **The Law of Segregation:** Each individual receives one allele for a trait from each parent. - **The Law of Independent Assortment:** Alleles for different traits segregate and assort independently of each other. ### Important Concepts - **Monohybrid cross:** Involves the inheritance of a single trait. - **Dihybrid cross:** Involves the inheritance of two traits simultaneously. - **Variation:** The differences within a species. - **Evolutionary mechanisms:** Processes by which species evolve over time. - **Natural Selection:** The process by which organisms with traits that make them better suited to their environment are more likely to survive and reproduce. - **Genetic drift:** Random changes in allele frequencies within a population. - **Mutation:** Changes in the DNA sequence that can lead to new traits. - **Adaptations:** Traits that make organisms better suited to their environment. ## Diseases - **Congenital diseases:** Present at birth due to abnormalities in genes or chromosomes. - **Acquired diseases:** Develop after birth as a result of infections or other factors. ### Types of Diseases - **Communicable diseases:** Infectious diseases that can be transmitted from one person to another. - **Bacterial diseases:** Caused by bacteria. - **Viral diseases:** Caused by viruses. - **Non-communicable diseases:** Not infectious. - **Heart attack:** Caused by blockage of blood flow to the heart. - **Diabetes:** Caused by the body's inability to regulate blood sugar levels. ### Deficiency Diseases - Occur due to lack of essential nutrients in the diet. - **Kwashiorkor:** Caused by a deficiency of protein, leading to stunted growth and edema (swelling). - **Marasmus:** Caused by a severe deficiency of calories and protein, leading to wasting and thinning of the body. - **Goiter:** Caused by a deficiency of iodine, leading to an enlarged thyroid gland in the neck. - **Anemia:** Caused by a deficiency of iron, leading to reduced red blood cell count and impaired oxygen-carrying capacity of the blood. - **Hypokalemia:** Caused by a deficiency of potassium, leading to muscle weakness, irregular heartbeat, and fatigue. - **Rickets:** Caused by a deficiency of vitamin D, leading to soft and weak bones in children. - **Scurvy:** Caused by a deficiency of vitamin C, leading to bleeding gums and impaired wound healing. ## Environmental Issues - **Pollution:** The contamination of the environment. - **Air pollution:** Caused by the release of harmful gases and particles into the atmosphere. - **Water pollution:** Caused by the release of pollutants substances into water bodies. - **Soil pollution:** Caused by the contamination of soil with harmful chemicals. - **Climate change:** The long-term shift in global weather patterns due to increased greenhouse gas emissions. - **Deforestation:** The clearing of forests. - **Biodiversity loss:** The decline in the variety of life on Earth. ## Conservation of Biodiversity - **Conservation:** The protection and management of natural resources and biodiversity. - Sustainable practices are essential for maintaining biodiversity and ensuring the well-being of future generations. ## Key Tips for Studying Biology - **Read the textbook thoroughly:** Don't just skim, try to fully understand the concepts. - **Make notes:** Writing down your key points will help you retain the information. - **Draw diagrams:** This will help you visualize the concepts. - **Practice labeling:** This will help you understand the different parts of structures. - **Answer past papers:** It will help you understand the exam pattern and get familiar with different question types. - **Review regularly:** Revisit your notes and practice questions frequently to solidify your understanding. - **Seek help when needed:** Don't be afraid to ask your teacher, friends, or peers for help if you are struggling.