Chloroplasts are organelles that conduct photosynthesis in plant cells, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water in plant and algal cells.
<em>Most trees do 'slow down' during winter, and deciduous trees that lose their leaves shut down photosynthesis entirely. Trees with needles (evergreen trees) that are retained over winter can actually photosynthesize during the winter.</em>
