Notes, abstracts, papers, exams and problems of Biology

Active transport is the movement of substances Across cell-membranes against a concentration gradient, from a region of low to A region of high concentration using energy from ATP.

Carrier mediated active transport

Carrier mediated active transport requires both energy (ATP) and the assistance of a transport protein, called pump.

Each pump only transports particular substances, so cells Can control what is absorbed and what is expelled. Pumps work in a specific Direction –the substance can only enter the

pump on one side and can only exit on the other side. Energy Is used to “pump” molecules across cell membranes against their concentration Gradients.

Vesicular active transport

Vesicular active transport is an energy-requiring Mechanism whereby... Continue reading "First cells and how they obtained energy" »

Biotic and Abiotic factors:

Ecosystem: all the living and nonliving parts of an environment.

Biotic factors: the living parts of an ecosystem.

Abiotic factors: the nonliving parts of an ecosystem.

Living things need non-living things to survive. Without food, water, and air, living things die. Sunlight (because provides energy that plants, and certain bacteria absorb to make their own food) shelter, and soil are also important for living things

Trees are biotic elements which need water that is an abiotic element. Without water the tree wouldn’t make oxygen, but without trees the water wouldn’t complete the water cycle.

Changes in abiotic factors can result in extreme problems for some organisms. For example, if a plant is adapted to low temperatures

Facial characteristics can be organised into three levels of facial features:

Level 1 details consist of gross facial characteristics that are easily observable. These include general geometry of the face and global skin colour. Such features can be used to quickly discriminate between a short round face and a long thin face, between predominantly male or female characteristics, and between faces from different races.Level 2 details consist of localised face information such as the structure of face components (e.G. Eyes), the relationship between facial components and the precise shape of the face. These features are essential for accurate recognition and require a higher resolution face image. The characteristics of local regions of the face... Continue reading "level" »

1) Tertiary crowding theories - lack of tooth wear, 3rd molar pression, late mandibular growth

Darwin and the theory of natural selection

The principal merit of Darwin's theory, in addition to the many evidence that he provided to it, is the discovery of the mechanism that governs the entire evolutionary process of species: the natural selection.

1) Firstly, when environmental resources become scarce, an inevitable competition occurs and, consequently, begin the struggle for survival in which most individuals die.

2) Secondly, it is also obvious that individuals of the same species have different features or characteristics that appear randomly and make individuals different each other.

 3) Third, these characteristics make some individuals more advantaged than others. Those whose characteristics are favourable to the demands of the environment... Continue reading "Fixism theory" »

PLANT CELLS:

• Have regular shape

• Have cell wall, chloroplasts (most of the cells, but not all), a big vacuole

A. Cell Wall:

• Made of cellulose

• Only in plant cells

• Helps to support and protect the cell

• Fully permeable (even very large molecules are able to go through the cellulose cell wall)
  
  

B. Vacuole:

• It is a space in a cell surrounded by a membrane and contain a solution of sugars and other substances called “cell sap”

• Full vacuoles press outwards on the rest of the cell and help to keep it in shape

• (animal cells contain much smaller vacuoles)

C. Chloroplasts:

• Never found in animal cells

• Present in Most of the plant cells

• Contain “Chlorophyll” (absorbs energy from sunlight, and this energy is then used for making food for the plant by “Photosynthesis”

• Often