Cells and control Revision Notes

Animal Growth: Cell Division and Differentiation

In animals, growth primarily occurs through cell division (mitosis), which increases the number of cells. This process is crucial for development from a zygote into a multicellular organism, and for repairing tissues and replacing dead cells throughout life. Cells then differentiate, meaning they become specialised to perform specific functions, such as nerve cells, muscle cells, or blood cells. Once an animal reaches its mature size, the rate of cell division for overall growth generally slows down significantly, although cell replacement for maintenance continues.

Plant Growth: Division, Elongation, and Differentiation

Plant growth is a continuous process occurring in specific regions known as meristems. These regions, such as the tips of roots and shoots, contain cells that undergo rapid cell division (mitosis), increasing the cell number. Following division, these new cells undergo cell elongation, where they absorb water and expand significantly, increasing the plant's size. Finally, these elongated cells differentiate into various specialised plant tissues, like xylem for water transport, phloem for nutrient transport, or epidermal cells for protection, contributing to the complete structure of the plant.

What is cell differentiation?

Cell differentiation is the process where a less specialised cell becomes a more specialised cell type, acquiring distinct structures and functions. This process is essential for the development and maintenance of multicellular organisms.

Importance in multicellular organisms

In multicellular organisms, differentiation allows cells to develop specific roles. This division of labour enables the organism to perform complex functions efficiently. It leads to the formation of specialised tissues and organs, each undertaking particular tasks vital for survival.

Embryonic development

During embryonic development, cells start as unspecialised stem cells. Through differentiation, they become various cell types like nerve cells, muscle cells, and skin cells. This ordered specialisation is crucial for the formation of a complete and functional organism.

Specialised cell functions

Specialised cells, such as nerve cells with their elongated structure for signal transmission or red blood cells lacking a nucleus for more oxygen transport, arise from differentiation. Their unique structures are adapted for their specific functions, underpinning the organism's physiological processes.

What are Percentile Charts?

Percentile charts are graphical tools used in healthcare to track physical growth (e.g., height, weight, head circumference) in children and adolescents. They compare a child's measurements to those of a large, healthy reference population of the same age and gender. Each line on the chart represents a percentile, indicating the proportion of the reference population that falls below that measurement.

Interpreting Percentiles

The 50th percentile line represents the average measurement. A child on the 75th percentile for weight means 75% of children of the same age and gender weigh less. Consistent growth along a percentile line is generally healthy. Significant deviations (e.g., crossing multiple percentile lines rapidly) can indicate potential health issues like undernutrition, overnutrition, or underlying medical conditions, requiring medical review.

Purpose of Growth Monitoring

Using percentile charts allows healthcare professionals to: 1. Identify normal growth patterns. 2. Detect deviations from expected growth early. 3. Monitor the effectiveness of nutritional or medical interventions. 4. Reassure parents about their child's development. Regular plotting helps to build a growth curve for individual children.

Embryonic Stem Cell Function

Embryonic stem cells are found in very early animal embryos. They are pluripotent, which means they can differentiate into almost every cell type in the body. Their primary function is to form all the tissues and organs during embryonic development, leading to the formation of a complete multi-cellular organism.

Adult Animal Stem Cell Function

Adult stem cells are found in some tissues and organs throughout an animal's life. They are multipotent, meaning they can differentiate into a limited range of cell types within specific tissues. Their main function is to replace dead or damaged cells, facilitating tissue repair and maintenance, such as blood cells from bone marrow stem cells.

Meristem Function in Plants

Meristems are regions in plants containing meristematic cells, which are plant stem cells. These cells are totipotent, meaning they can differentiate into any plant cell type. Meristems are responsible for the plant's continuous growth, forming new stems, roots, leaves, and flowers throughout its lifespan. Examples include apical meristems at shoot and root tips, and lateral meristems for girth.