Inclusive tuition for the top ten percentile of PSLE Science students. P5 Topic Cells for PSLE 2014 Science syllabus, Primary 5 Science Topic Cells. This guide is specific to Singapore MOE SEAB PSLE Science 2014 Syllabus.

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Cells

A cell is a basic unit of life. It is the basic building blocks that makes all living things. Cells come from other cells, splitting into identical cells in a process called Mitosis. These daughter cells have identical replicates of chromosomes.

Another process called Meiosis is a special process of producing cells for reproduction like sperm cells and egg cells that have half the normal chromosomes.

Cells are the functional and structural units of living organisms that are needed for growth, reproduction and sustaining life. Cells can exist as single-cellular organisms (prokaryotic cells) to a myriad of multi-cellular organisms (eukaryotic cells)

Cells are small compartments that hold all the biological materials needed to carry out the function of life. It has specialised structures called organelles with distinct functions that help the cell to operate. Different combinations of organelles will create a cell with a different function to the organism. If a cell’s compartment breaks or an organelle is missing or fails, the cell will then die.

Summary so far

Plant cells and Animal cells.

There are two types of cells, plant cells and animals cells. Plant cells have a cell wall that protects the cell from injury. It also has organelles called chloroplast that conduct photosynthesis.

Main Parts of a plant cell:

1. Cell wall
2. Cell membrane
3. Chloroplast
4. Cytoplasm
5. Nucleus
6. Vacuole

Main Parts of an animal cell:

1. Cell membrane
2. Cytoplasm
3. Nucleus
4. Vacuole

Plant Cells

Chloroplast: A special organelle

Found in plant cells and eukaryotic algae that conducts photosynthesis. It uses the pigment chlorophyll that absorbs sunlight energy with presence of water and carbon dioxide to produce energy storage molecules ATP and NADPH whilst freeing oxygen from water.

Cell Wall

Cell walls are only found in plant cells and surrounds a cell membrane, Made of cellulose, it protects the plant cell, filtering nutrients and maintains the shape of the plant to support plant parts. (the equivalent of the skeletal structure in animals) It also provides elasticity to plants, helping plants to bend in the wind or move its leaves in the direction of sunlight.

Cell walls can be tough, flexible and rigid. It helps prevent over pressure of plant cells, keeping the cell from over expansion. Up to three cell walls can be found in plant cells.

Cells walls have small holes called plasmodesmata in it that allows waste and nutrients to pass. It is also the reason during a drought, where water can be lost to the surrounding, the cell loses its turgidity and leaves the plant limp. However, the cell wall will still maintain its basic shape and will be filled back to its original shape when there is presence of water.

1. found only in plants
2. made of cellulose
3. protects the plant cell
4. support and maintains the shape of plants

Cell Membrane

Cell membrane separates the interior of a cell from its surrounding. Like our skin, it acts as a barrier to the environment and protects the cell. It also controls the movement substances into and out of the cell. (for example oxygen, carbon dioxide and steroids) It is composed of lipids and proteins

Mitochondria

Mitochondria are the organelles of a cell that take in nutrients, break it down and produce energy for the cell in a process known as cellular respiration. As the powerhouses of the cell, chemical reactions within the cell produces the energy in a two membrane organelle, as compared to others with only one membrane.

The outer membranes protects and covers the inner membrane. The inner membrane is shaped perfectly in folds to increase surface area that increases the rate of chemical reactions. The fluid inside is called the matrix.

Vacuole

A vacuole is a membrane bound organelle that is present in all plant cells and some animal cells. It is larger in plant cells than animal cells. Vacuoles contain water, nutrients and waste products. (Organic, inorganic molecules including enzymes)

Vacuoles have no basic shape or size, with its variance in accordance to the requirements of the cell. Like cell walls, vacuoles also provides support and maintains the cell structure for the plant cell.

1. contains water
2. contains waste product
3. exports waste product out of the cell
4. filters out harmful materials
5. maintains turgidity in plants
6. can increase size to quickly grow a plant

Cytoplasm

Cytoplasm is all of the material inside a cell minus the cell nucleus. The main component is a gel like substance cytosol which is made of 80% watering usually colorless, with organelles making up the rest of cytoplasm.

Nucleus

The nucleus of a cell is the control centre and acts as the manager of the cell. It  contains information and gives instructions to other organelles to function within the cell. It also stores hereditary genetic information, DNA, that allows cell division and reproduce. Only advanced eukaryote cells have a nucleus. It usually occupies 10% of the space within a cell.

Special Cells for Plants

Root Hair Cell

Root Hair Cells are specialised cells with no chloroplast as there is no light in the ground. It has a structure for absorbing more water and minerals from the soil with long projections, hence an increase in surface area to help in absorption.

Guard Cell

Guard cells are found on the epidermis of the leaves, stems and parts of a plant that requires gaseous exchange. Usually found as a pair, guard cells form a stomatal pore, with the ability to open and close to regulate gaseous exchange. The opening and closing of the stomata are controlled by water concentration moving into the cell.

When water moves into the guard cell, it swells up and the stomata opens to allow gaseous exchange since plants respire throughout the day. The gap needed for photosynthesis is bigger in the day to allow more carbon dioxide in and oxygen out, while at night, with no need for photosynthesis, the gap will be small but allow enough oxygen in for respiration.

However, a wide open stoma will also allow water vapour to escape from the plant and requires transpiration from the roots to replenish the plant. If water availability is critically low, for example, during a drought, water will start leaving the guard cells and close the stoma opening, stopping further water losses. This helps protect the plant from dehydration.

Differences of plant cells and animal cells

Plant cells and animal cells are both eukaryotic so both contain the nucleus and have membrane bound organelles. However, there are differences as they require different organelles to perform different functions.

1. Plant cells have large vacuole, animal cells have small vacuoles.
2. Plant cells have few vacuoles, animal cells can have numerous vacuoles.
3. Plant cells have cell walls, animal cells do not.
4. Plant cells contain chloroplast for photosynthesis, animal cells do not.
5. Due to a lack of cell wall, animal cells can come in a lot of different shapes and sizes leading to different functions.

Cell division

Cells divide and replicate itself. This allows living things to grow, reproduce heal and replace worn-out/dead cells. The two types of cell divine are mitosis and meiosis.

Animal cells can arrange itself to perform specialised functions. It can replicate and the nucleus contains DNA information to organise itself to make organs like kidney or the heart.

How is a human cell made?

Human Blood

Blood contains four main components:

1. red blood cell
2. white blood cell
3. plasma
4. platelets

It carries out many functions including

• transporting oxygen and nutrients/energy throughout the body
• removing carbon dioxide from body tissues
• forming blood clots to stop bleeding
• carrying cells and antibodies to fight infection and heal
• transport and remove waste material to be filtered out by kidneys and liver.
• regulating body temperature

Blood cells are formed from stem cells in the bone marrow.

Red Blood Cells

Red in color when it is oxygen rich, accounts for 40-45 percent of blood volume, shaped biconcave to increase surface area to aid in gaseous exchange. It has no nucleus and allows the cell to be flexible and easily change shape to reach every corner of the body. However, that limits the lifespan of red blood cells to approximately 120 days. 2 million red bloods are produced every second.

It carries a protein hemoglobin that carries oxygen from the lungs to the body and exchange for carbon dioxide back to the lungs to be disposed.

White Blood Cells

White blood cells are the army of the body, protecting the body from infection by overcoming bacteria and viruses. Much smaller in concentration than red blood cells, with 1% of blood volume, white blood cells consists of neutrophils, T. lymphocyte and B. lymphocyte.

Single Cell Organisms

Extra Information